Anarchism is a political philosophy and movement that is skeptical of all justifications for authority and seeks to abolish the institutions they claim maintain unnecessary coercion and hierarchy, typically including, though not necessarily limited to, governments, nation states, and capitalism. Anarchism advocates for the replacement of the state with stateless societies or other forms of free associations. As a historically left-wing movement, usually placed on the farthest left of the political spectrum, it is usually described alongside communalism and libertarian Marxism as the libertarian wing (libertarian socialism) of the socialist movement.

Humans lived in societies without formal hierarchies long before the establishment of formal states, realms, or empires. With the rise of organised hierarchical bodies, scepticism toward authority also rose. Although traces of anarchist thought are found throughout history, modern anarchism emerged from the Enlightenment. During the latter half of the 19th and the first decades of the 20th century, the anarchist movement flourished in most parts of the world and had a significant role in workers' struggles for emancipation. Various anarchist schools of thought formed during this period. Anarchists have taken part in several revolutions, most notably in the Paris Commune, the Russian Civil War and the Spanish Civil War, whose end marked the end of the classical era of anarchism. In the last decades of the 20th and into the 21st century, the anarchist movement has been resurgent once more, growing in popularity and influence within anti-capitalist, anti-war and anti-globalisation movements.

Anarchism employs a diversity of tactics in order to meet its ideal ends which can be broadly separated into revolutionary and evolutionary tactics; there is significant overlap between the two, which are merely descriptive. Revolutionary tactics aim to bring down authority and state, having taken a violent turn in the past, while evolutionary tactics aim to prefigure what an anarchist society would be like. Anarchist thought, criticism, and praxis have played a part in diverse areas of human society.

The most common critique of anarchism is that humans cannot self-govern and so a state is necessary for human survival. Philosopher Bertrand Russell supported this critique, stating that "[p]eace and war, tariffs, regulations of sanitary conditions and the sale of noxious drugs, the preservation of a just system of distribution: these, among others, are functions which could hardly be performed in a community in which there was no central government." Another common criticism of anarchism is that it fits a world of isolation in which only the small enough entities can be self-governing; a response would be that major anarchist thinkers advocated anarchist federalism.

Philosophy lecturer Andrew G. Fiala composed a list of common arguments against anarchism which includes critiques such as that anarchism is innately related to violence and destruction, not only in the pragmatic world, such as at protests, but in the world of ethics as well. Secondly, anarchism is evaluated as unfeasible or utopian since the state cannot be defeated practically. This line of arguments most often calls for political action within the system to reform it. The third argument is that anarchism is self-contradictory as a ruling theory that has no ruling theory. Anarchism also calls for collective action whilst endorsing the autonomy of the individual, hence no collective action can be taken. Lastly, Fiala mentions a critique towards philosophical anarchism of being ineffective (all talk and thoughts) and in the meantime capitalism and bourgeois class remains strong.

Philosophical anarchism has met the criticism of members of academia following the release of pro-anarchist books such as A. John Simmons' Moral Principles and Political Obligations. Law professor William A. Edmundson authored an essay to argue against three major philosophical anarchist principles which he finds fallacious. Edmundson says that while the individual does not owe the state a duty of obedience, this does not imply that anarchism is the inevitable conclusion and the state is still morally legitimate. In The Problem of Political Authority, Michael Huemer defends philosophical anarchism, claiming that "political authority is a moral illusion."

One of the earliest criticisms is that anarchism defies and fails to understand the biological inclination to authority. Joseph Raz states that the acceptance of authority implies the belief that following their instructions will afford more success. Raz believes that this argument is true in following both authorities' successful and mistaken instruction. Anarchists reject this criticism because challenging or disobeying authority does not entail the disappearance of its advantages by acknowledging authority such as doctors or lawyers as reliable, nor does it involve a complete surrender of independent judgment. Anarchist perception of human nature, rejection of the state, and commitment to social revolution has been criticised by academics as naive, overly simplistic, and unrealistic, respectively. Classical anarchism has been criticised for relying too heavily on the belief that the abolition of the state will lead to human cooperation prospering.

Friedrich Engels, considered to be one of the principal founders of Marxism, criticised anarchism's anti-authoritarianism as inherently counter-revolutionary because in his view a revolution is by itself authoritarian. Academic John Molyneux writes in his book Anarchism: A Marxist Criticism that "anarchism cannot win", believing that it lacks the ability to properly implement its ideas. The Marxist criticism of anarchism is that it has a utopian character because all individuals should have anarchist views and values. According to the Marxist view, that a social idea would follow directly from this human ideal and out of the free will of every individual formed its essence. Marxists state that this contradiction was responsible for their inability to act. In the anarchist vision, the conflict between liberty and equality was resolved through coexistence and intertwining.


In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing calculations and data processing. More advanced algorithms can perform automated deductions (referred to as automated reasoning) and use mathematical and logical tests to divert the code execution through various routes (referred to as automated decision-making). Using human characteristics as descriptors of machines in metaphorical ways was already practiced by Alan Turing with terms such as "memory", "search" and "stimulus".

In contrast, a heuristic is an approach to problem solving that may not be fully specified or may not guarantee correct or optimal results, especially in problem domains where there is no well-defined correct or optimal result.

As an effective method, an algorithm can be expressed within a finite amount of space and time, and in a well-defined formal language for calculating a function. Starting from an initial state and initial input (perhaps empty), the instructions describe a computation that, when executed, proceeds through a finite number of well-defined successive states, eventually producing "output" and terminating at a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate random input.

The concept of algorithm has existed since antiquity. Arithmetic algorithms, such as a division algorithm, were used by ancient Babylonian mathematicians c. 2500 BC and Egyptian mathematicians c. 1550 BC. Greek mathematicians later used algorithms in 240 BC in the sieve of Eratosthenes for finding prime numbers, and the Euclidean algorithm for finding the greatest common divisor of two numbers. Arabic mathematicians such as al-Kindi in the 9th century used cryptographic algorithms for code-breaking, based on frequency analysis.

The word algorithm is derived from the name of the 9th-century Persian mathematician Muḥammad ibn Mūsā al-Khwārizmī, whose nisba (identifying him as from Khwarazm) was Latinized as Algoritmi (Arabized Persian الخوارزمی c. 780–850).
Muḥammad ibn Mūsā al-Khwārizmī was a mathematician, astronomer, geographer, and scholar in the House of Wisdom in Baghdad, whose name means 'the native of Khwarazm', a region that was part of Greater Iran and is now in Uzbekistan. About 825, al-Khwarizmi wrote an Arabic language treatise on the Hindu–Arabic numeral system, which was translated into Latin during the 12th century. The manuscript starts with the phrase Dixit Algorizmi ('Thus spake Al-Khwarizmi'), where "Algorizmi" was the translator's Latinization of Al-Khwarizmi's name. Al-Khwarizmi was the most widely read mathematician in Europe in the late Middle Ages, primarily through another of his books, the Algebra. In late medieval Latin, algorismus, English 'algorism', the corruption of his name, simply meant the "decimal number system". In the 15th century, under the influence of the Greek word ἀριθμός (arithmos), 'number' (cf. 'arithmetic'), the Latin word was altered to algorithmus, and the corresponding English term 'algorithm' is first attested in the 17th century; the modern sense was introduced in the 19th century.

Indian mathematics was predominantly algorithmic.
Algorithms that are representative of the Indian mathematical tradition range from the ancient Śulbasūtrās to the medieval texts of the Kerala School.

In English, the word algorithm was first used in about 1230 and then by Chaucer in 1391. English adopted the French term, but it was not until the late 19th century that "algorithm" took on the meaning that it has in modern English.

Another early use of the word is from 1240, in a manual titled Carmen de Algorismo composed by Alexandre de Villedieu. It begins with:

which translates to:

The poem is a few hundred lines long and summarizes the art of calculating with the new styled Indian dice (Tali Indorum), or Hindu numerals.

A partial formalization of the modern concept of algorithm began with attempts to solve the Entscheidungsproblem  (decision problem) posed by David Hilbert in 1928. Later formalizations were framed as attempts to define "effective calculability" or "effective method". Those formalizations included the Gödel–Herbrand–Kleene recursive functions of 1930, 1934 and 1935, Alonzo Church's lambda calculus of 1936, Emil Post's Formulation 1 of 1936, and Alan Turing's Turing machines of 1936–37 and 1939.


Alexander III of Macedon (; 20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great, was a king of the ancient Greek kingdom of Macedon. He succeeded his father Philip II to the throne in 336 BC at the age of 20, and spent most of his ruling years conducting a lengthy military campaign throughout Western Asia and Egypt. By the age of thirty, he had created one of the largest empires in history, stretching from Greece to northwestern India. He was undefeated in battle and is widely considered to be one of history's greatest and most successful military commanders.

Until the age of 16, Alexander was tutored by Aristotle. In 335 BC, shortly after his assumption of kingship over Macedon, he campaigned in the Balkans and reasserted control over Thrace and Illyria before marching on the city of Thebes, which was subsequently destroyed in battle. Alexander then led the League of Corinth, and used his authority to launch the pan-Hellenic project envisaged by his father, assuming leadership over all Greeks in their conquest of Persia.

In 334 BC, he invaded the Achaemenid Persian Empire and began a series of campaigns that lasted for 10 years. Following his conquest of Asia Minor, Alexander broke the power of Achaemenid Persia in a series of decisive battles, including those at Issus and Gaugamela; he subsequently overthrew Darius III and conquered the Achaemenid Empire in its entirety. After the fall of Persia, the Macedonian Empire held a vast swath of territory between the Adriatic Sea and the Indus River. Alexander endeavored to reach the "ends of the world and the Great Outer Sea" and invaded India in 326 BC, achieving an important victory over Porus, an ancient Indian king of present-day Punjab, at the Battle of the Hydaspes. Due to the demand of his homesick troops, he eventually turned back at the Beas River and later died in 323 BC in Babylon, the city of Mesopotamia that he had planned to establish as his empire's capital. Alexander's death left unexecuted an additional series of planned military and mercantile campaigns that would have begun with a Greek invasion of Arabia. In the years following his death, a series of civil wars broke out across the Macedonian Empire, eventually leading to its disintegration at the hands of the Diadochi.

With his death marking the start of the Hellenistic period, Alexander's legacy includes the cultural diffusion and syncretism that his conquests engendered, such as Greco-Buddhism and Hellenistic Judaism. He founded more than twenty cities that bore his name, with the most prominent being the city of Alexandria in Egypt. Alexander's settlement of Greek colonists and the resulting spread of Greek culture led to the overwhelming dominance of Hellenistic civilization and influence as far east as the Indian subcontinent. The Hellenistic period developed through the Roman Empire into modern Western culture; the Greek language became the lingua franca of the region and was the predominant language of the Byzantine Empire up until its collapse in the mid-15th century AD. Greek-speaking communities in central Anatolia and in far-eastern Anatolia survived until the Greek genocide of the 1910s and early 1920s as well as the Greek–Turkish population exchange of the mid-1920s. Alexander became legendary as a classical hero in the mould of Achilles, featuring prominently in the historical and mythical traditions of both Greek and non-Greek cultures. His military achievements and unprecedented enduring successes in battle made him the measure against which many later military leaders would compare themselves, and his tactics remain a significant subject of study in military academies worldwide.

Apart from a few inscriptions and fragments, texts written by people who actually knew Alexander or who gathered information from men who served with Alexander were all lost. Contemporaries who wrote accounts of his life included Alexander's campaign historian Callisthenes; Alexander's generals Ptolemy and Nearchus; Aristobulus, a junior officer on the campaigns; and Onesicritus, Alexander's chief helmsman. Their works are lost, but later works based on these original sources have survived. The earliest of these is Diodorus Siculus (1st century BC), followed by Quintus Curtius Rufus (mid-to-late 1st century AD), Arrian (1st to 2nd century AD), the biographer Plutarch (1st to 2nd century AD), and finally Justin, whose work dated as late as the 4th century. Of these, Arrian is generally considered the most reliable, given that he used Ptolemy and Aristobulus as his sources, closely followed by Diodorus.


An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. Common examples of aircraft include airplanes, helicopters, airships (including blimps), gliders, paramotors, and hot air balloons.

The human activity that surrounds aircraft is called aviation. The science of aviation, including designing and building aircraft, is called aeronautics. Crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as lift type, aircraft propulsion, usage and others.

The Evolution of Modern Aircraft (NASA)
 Virtual Museum
 Smithsonian Air and Space Museum - online collection with a particular focus on history of aircraft and spacecraft
 Amazing Early Flying Machines  slideshow by Life magazine


The afterlife (also referred to as life after death) is a purported existence in which the essential part of an individual's identity or their stream of consciousness continues to live after the death of their physical body. The surviving essential aspect varies between belief systems; it may be some partial element, or the entire soul or spirit of an individual, which carries with it and may confer personal identity or, on the contrary, nirvana. Belief in an afterlife is in contrast to the belief in oblivion after death.

In some views, this continued existence takes place in a spiritual realm, while in others,  the individual may be reborn into this world and begin the life cycle over again, likely with no memory of what they have done in the past. In this latter view, such rebirths and deaths may take place over and over again continuously until the individual gains entry to a spiritual realm or otherworld. Major views on the afterlife derive from religion, esotericism and metaphysics.

Some belief systems, such as those in the Abrahamic tradition, hold that the dead go to a specific place after death, as determined by God, or other divine judgment, based on their actions or beliefs during life. In contrast, in systems of reincarnation, such as those in the Indian religions, the nature of the continued existence is determined directly by the actions of the individual in the ended life.

Theists generally believe some afterlife awaits people when they die. Members of some generally non-theistic religions tend to believe in an afterlife but without reference to a deity. The Sadducees were an ancient Jewish sect that generally believed that there was a God but no existence after death.

Many religions, whether they believe in the soul's existence in another world like Christianity, Islam, and many pagan belief systems, or reincarnation like many forms of Hinduism and Buddhism, believe that one's status in the afterlife is a consequence of one's conduct during life.


An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenza; drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics.

Sometimes, the term antibiotic—literally "opposing life", from the Greek roots ἀντι anti, "against" and βίος bios, "life"—is broadly used to refer to any substance used against microbes, but in the usual medical usage, antibiotics (such as penicillin) are those produced naturally (by one microorganism fighting another), whereas non-antibiotic antibacterials (such as sulfonamides and antiseptics) are fully synthetic. However, both classes have the same goal of killing or preventing the growth of microorganisms, and both are included in antimicrobial chemotherapy. "Antibacterials" include antiseptic drugs, antibacterial soaps, and chemical disinfectants, whereas antibiotics are an important class of antibacterials used more specifically in medicine and sometimes in livestock feed.

Antibiotics have been used since ancient times. Many civilizations used topical application of moldy bread, with many references to its beneficial effects arising from ancient Egypt, Nubia, China, Serbia, Greece, and Rome. The first person to directly document the use of molds to treat infections was John Parkinson (1567–1650). Antibiotics revolutionized medicine in the 20th century. Alexander Fleming (1881–1955) discovered modern day penicillin in 1928, the widespread use of which proved significantly beneficial during wartime. However, the effectiveness and easy access to antibiotics have also led to their overuse and some bacteria have evolved resistance to them. The World Health Organization has classified antimicrobial resistance as a widespread "serious threat [that] is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country". Global deaths attributable to antimicrobial resistance numbered 1.27 million in 2019.

Antibiotics are screened for any negative effects before their approval for clinical use, and are usually considered safe and well tolerated. However, some antibiotics have been associated with a wide extent of adverse side effects ranging from mild to very severe depending on the type of antibiotic used, the microbes targeted, and the individual patient. Side effects may reflect the pharmacological or toxicological properties of the antibiotic or may involve hypersensitivity or allergic reactions. Adverse effects range from fever and nausea to major allergic reactions, including photodermatitis and anaphylaxis.

Common side effects of oral antibiotics include diarrhea, resulting from disruption of the species composition in the intestinal flora, resulting, for example, in overgrowth of pathogenic bacteria, such as Clostridium difficile. Taking probiotics during the course of antibiotic treatment can help prevent antibiotic-associated diarrhea. Antibacterials can also affect the vaginal flora, and may lead to overgrowth of yeast species of the genus Candida in the vulvo-vaginal area. Additional side effects can result from interaction with other drugs, such as the possibility of tendon damage from the administration of a quinolone antibiotic with a systemic corticosteroid.

Some antibiotics may also damage the mitochondrion, a bacteria-derived organelle found in eukaryotic, including human, cells. Mitochondrial damage cause oxidative stress in cells and has been suggested as a mechanism for side effects from fluoroquinolones. They are also known to affect chloroplasts.


Board games are tabletop games that typically use . These pieces are moved or placed on a pre-marked board (playing surface) and often include elements of table, card, role-playing, and miniatures games as well.

Many board games feature a competition between two or more players. To show a few examples: in checkers (British English name 'draughts'), a player wins by capturing all opposing pieces, while Eurogames often end with a calculation of final scores. Pandemic is a cooperative game where players all win or lose as a team, and peg solitaire is a puzzle for one person.

There are many varieties of board games. Their representation of real-life situations can range from having no inherent theme, such as checkers, to having a specific theme and narrative, such as Cluedo. Rules can range from the very simple, such as in Snakes and Ladders; to deeply complex, as in Advanced Squad Leader. Play components now often include custom figures or shaped counters, and distinctively shaped player pieces commonly known as meeples as well as traditional cards and dice.

The time required to learn or master game play varies greatly from game to game, but is not necessarily related to the number or complexity of rules, and games like chess or Go possess relatively simple , but have great strategic depth.

There are a number of ways in which board games can be classified, and considerable overlap may exist, so that a game belong in several categories.

H. J. R. Murray's A History of Board Games Other Than Chess (1952) has been called the first attempt to develop a "scheme for the classification of board games". David Parlett's Oxford History of Board Games (1999) defines four primary categories: race games (where the goal is to be the first to move all one's pieces to the final destination), space games (in which the object is to arrange the pieces into some special configuration), chase games (asymmetrical games, where players start the game with different sets of pieces and objectives) and displace games (where the main objective is the capture the opponents' pieces). Parlett's also distinguishes between abstract and thematic games, the latter having a specific theme or frame narrative (ex. regular chess versus, for example, Star Wars-themed chess).

The following is a list of some of the most common game categories:

 Abstract strategy games – e.g. Chess, Checkers, Go, Reversi, tafl games, or modern games such as Abalone, Dameo, Stratego, Hive, or GIPF
 Alignment games – e.g. Renju, Gomoku, Connect6, Nine men's morris, or Tic-tac-toe
 Auction games – e.g. Hoity Toity, Power Grid
 Chess variants – traditional variants e.g. shogi, xiangqi, or janggi; modern variants e.g. Chess960, Grand Chess, Hexagonal chess, or Alice Chess
 Configuration games – e.g. Lines of Action, Hexade, or Entropy
 Connection games – e.g. TwixT, Hex, or Havannah
 Cooperative games – e.g. Max the Cat, Caves and Claws, or Pandemic
 Count and capture games – e.g. mancala games
 Cross and circle games – e.g. Yut, Ludo, or Aggravation
 Deduction games – e.g. Mastermind or Black Box
 Dexterity games – e.g. Tumblin' Dice or Pitch Car
 Economic simulation games – e.g. The Business Game, Monopoly, The Game of Life, Power Grid, or Food Chain Magnate
 Educational games – e.g. Arthur Saves the Planet, Cleopatra and the Society of Architects, or Shakespeare: The Bard Game
 Elimination games – e.g. draughts, Alquerque, Fanorona, Yoté, or Surakarta
 Family games – e.g. Roll Through the Ages, Birds on a Wire, or For Sale
 Fantasy games – e.g. Shadows Over Camelot
 German-style board games or Eurogames – e.g. Catan, Carcassonne, Decatur • The Game, Carson City, or Puerto Rico
 Guessing games – e.g. Pictionary or Battleship
 Hidden-movement games – e.g. Clue or Escape from the Aliens in Outer Space
 Hidden-role games – e.g. Mafia or The Resistance
 Historical simulation games – e.g. Through the Ages or Railways of the World
 Horror games – e.g. Arkham Horror
 Large multiplayer games – e.g. Take It Easy or Swat (2010)
 Learning/communication non-competitive games – e.g. The Ungame (1972)
 Mancala games – e.g. Wari, Oware, or The Glass Bead Game
 Multiplayer games – e.g. Risk, Monopoly, or Four-player chess
 Musical games – e.g. Spontuneous
 Negotiation games – e.g. Diplomacy
 Paper-and-pencil games – e.g. Tic-tac-toe or Dots and Boxes
 Physical skill games – e.g. Camp Granada
 Position games (no captures; win by leaving the opponent unable to move) – e.g. Kōnane, mū tōrere, or the L game
 Race games – e.g. Pachisi, backgammon, Snakes and Ladders, Hyena chase, or Worm Up
 Role-playing games – e.g. Dungeons & Dragons
 Roll-and-move games – e.g. Monopoly or Life
 Running-fight games – e.g. Bul
 Share-buying games (games in which players buy stakes in each other's positions) – typically longer economic-management games, e.g. Acquire or Panamax
 Single-player puzzle games – e.g. peg solitaire or Sudoku
 Spiritual development games (games with no winners or losers) – e.g. Transformation Game or Psyche's Key
 Stacking games – e.g. Lasca or DVONN
  Storytelling games – e.g. Dixit or Tales of the Arabian Nights
 Territory games – e.g. Go or Reversi
 Tile-based games – e.g. Carcassonne, Scrabble, Tigris and Euphrates, or Evo
 Train games – e.g. Ticket to Ride, Steam, or 18xx
 Trivia games – e.g. Trivial Pursuit
 Two-player-only themed games – e.g. En Garde or Dos de Mayo
 Unequal forces (or "hunt") games – e.g. Fox and Geese or Tablut
 Wargames – ranging from Risk, Diplomacy, or Axis & Allies, to Attack! or Conquest of the Empire
 Word games – e.g. Scrabble, Boggle, Anagrams, or What's My Word? (2010)


Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts there of and molecular analogues for products and services. The term biotechnology was first used by Károly Ereky in 1919, meaning the production of products from raw materials with the aid of living organisms.

The concept of biotechnology encompasses a wide range of procedures for modifying living organisms according to human purposes, going back to domestication of animals, cultivation of the plants, and "improvements" to these through breeding programs that employ artificial selection and hybridization. Modern usage also includes genetic engineering as well as cell and tissue culture technologies. The American Chemical Society defines biotechnology as the application of biological organisms, systems, or processes by various industries to learning about the science of life and the improvement of the value of materials and organisms such as pharmaceuticals, crops, and livestock. As per the European Federation of Biotechnology, biotechnology is the integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services. Biotechnology is based on the basic biological sciences (e.g., molecular biology, biochemistry, cell biology, embryology, genetics, microbiology) and conversely provides methods to support and perform basic research in biology.

Biotechnology is the research and development in the laboratory using bioinformatics for exploration, extraction, exploitation, and production from any living organisms and any source of biomass by means of biochemical engineering where high value-added products could be planned (reproduced by biosynthesis, for example), forecasted, formulated, developed, manufactured, and marketed for the purpose of sustainable operations (for the return from bottomless initial investment on R & D) and gaining durable patents rights (for exclusives rights for sales, and prior to this to receive national and international approval from the results on animal experiment and human experiment, especially on the pharmaceutical branch of biotechnology to prevent any undetected side-effects or safety concerns by using the products). The utilization of biological processes, organisms or systems to produce products that are anticipated to improve human lives is termed biotechnology.

By contrast, bioengineering is generally thought of as a related field that more heavily emphasizes higher systems approaches (not necessarily the altering or using of biological materials directly) for interfacing with and utilizing living things. Bioengineering is the application of the principles of engineering and natural sciences to tissues, cells, and molecules. This can be considered as the use of knowledge from working with and manipulating biology to achieve a result that can improve functions in plants and animals. Relatedly, biomedical engineering is an overlapping field that often draws upon and applies biotechnology (by various definitions), especially in certain sub-fields of biomedical or chemical engineering such as tissue engineering, biopharmaceutical engineering, and genetic engineering.


Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flow under atmospheric pressure, and can be thought of as artificial rivers.

In most cases, a canal has a series of dams and locks that create reservoirs of low speed current flow. These reservoirs are referred to as slack water levels, often just called levels. A canal can be called a navigation canal when it parallels a natural river and shares part of the latter's discharges and drainage basin, and leverages its resources by building dams and locks to increase and lengthen its stretches of slack water levels while staying in its valley.

A canal can cut across a drainage divide atop a ridge, generally requiring an external water source above the highest elevation. The best-known example of such a canal is the Panama Canal.

Many canals have been built at elevations, above valleys and other waterways. Canals with sources of water at a higher level can deliver water to a destination such as a city where water is needed. The Roman Empire's aqueducts were such water supply canals.

Canals are built in one of three ways, or a combination of the three, depending on available water and available path:
Human made streams
 A canal can be created where no stream presently exists. Either the body of the canal is dug or the sides of the canal are created by making dykes or levees by piling dirt, stone, concrete or other building materials. The finished shape of the canal as seen in cross section is known as the canal prism. The water for the canal must be provided from an external source, like streams or reservoirs. Where the new waterway must change elevation engineering works like locks, lifts or elevators are constructed to raise and lower vessels. Examples include canals that connect valleys over a higher body of land, like Canal du Midi, Canal de Briare and the Panama Canal.
 A canal can be constructed by dredging a channel in the bottom of an existing lake. When the channel is complete, the lake is drained and the channel becomes a new canal, serving both drainage of the surrounding polder and providing transport there. Examples include the . One can also build two parallel dikes in an existing lake, forming the new canal in between, and then drain the remaining parts of the lake. The eastern and central parts of the North Sea Canal were constructed in this way. In both cases pumping stations are required to keep the land surrounding the canal dry, either pumping water from the canal into surrounding waters, or pumping it from the land into the canal.
Canalization and navigations

 A stream can be canalized to make its navigable path more predictable and easier to maneuver. Canalization modifies the stream to carry traffic more safely by controlling the flow of the stream by dredging, damming and modifying its path. This frequently includes the incorporation of locks and spillways, that make the river a navigation. Examples include the Lehigh Canal in Northeastern Pennsylvania's coal Region, Basse Saône, Canal de Mines de Fer de la Moselle, and Aisne River. Riparian zone restoration may be required.

Lateral canals
 When a stream is too difficult to modify with canalization, a second stream can be created next to or at least near the existing stream. This is called a lateral canal, and may meander in a large horseshoe bend or series of curves some distance from the source waters stream bed lengthening the effective length in order to lower the ratio of rise over run (slope or pitch). The existing stream usually acts as the water source and the landscape around its banks provide a path for the new body. Examples include the Chesapeake and Ohio Canal, Canal latéral à la Loire, Garonne Lateral Canal, Welland Canal and Juliana Canal.

Smaller transportation canals can carry barges or narrowboats, while ship canals allow seagoing ships to travel to an inland port (e.g., Manchester Ship Canal), or from one sea or ocean to another (e.g., Caledonian Canal, Panama Canal).


In mathematics, a complex number is an element of a number system that extends the real numbers with a specific element denoted , called the imaginary unit and satisfying the equation ; every complex number can be expressed in the form , where  and  are real numbers. Because no real number satisfies the above equation,  was called an imaginary number by René Descartes. For the complex number ,  is called the  and  is called the . The set of complex numbers is denoted by either of the symbols  or . Despite the historical nomenclature "imaginary", complex numbers are regarded in the mathematical sciences as just as "real" as the real numbers and are fundamental in many aspects of the scientific description of the natural world.

Complex numbers allow solutions to all polynomial equations, even those that have no solutions in real numbers. More precisely, the fundamental theorem of algebra asserts that every non-constant polynomial equation with real or complex coefficients has a solution which is a complex number. For example, the equation

has no real solution, since the square of a real number cannot be negative, but has the two nonreal complex solutions  and .

Addition, subtraction and multiplication of complex numbers can be naturally defined by using the rule  combined with the associative, commutative and distributive laws. Every nonzero complex number has a multiplicative inverse. This makes the complex numbers a field that has the real numbers as a subfield. The complex numbers also form a real vector space of dimension two, with  as a standard basis.

This standard basis makes the complex numbers a Cartesian plane, called the complex plane. This allows a geometric interpretation of the complex numbers and their operations, and conversely expressing in terms of complex numbers some geometric properties and constructions. For example, the real numbers form the real line which is identified to the horizontal axis of the complex plane. The complex numbers of absolute value one form the unit circle. The addition of a complex number is a translation in the complex plane, and the multiplication by a complex number is a similarity centered at the origin. The complex conjugation is the reflection symmetry with respect to the real axis. The complex absolute value is a Euclidean norm.

In summary, the complex numbers form a rich structure that is simultaneously an algebraically closed field, a commutative algebra over the reals, and a Euclidean vector space of dimension two.

A real number  can be regarded as a complex number , whose imaginary part is 0. A purely imaginary number  is a complex number , whose real part is zero. As with polynomials, it is common to write  for  and  for . Moreover, when the imaginary part is negative, that is, , it is common to write  instead of ; for example, for ,  can be written instead of .

Since the multiplication of the indeterminate  and a real is commutative in polynomials with real coefficients, the polynomial  may be written as  This is often expedient for imaginary parts denoted by expressions, for example, when  is a radical.

The real part of a complex number  is denoted by , , or ; the imaginary part of a complex number  is denoted by , , or  For example,

The set of all complex numbers is denoted by  (blackboard bold) or  (upright bold).

In some disciplines, particularly in electromagnetism and electrical engineering,  is used instead of  as  is frequently used to represent electric current. In these cases, complex numbers are written as , or .


A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.

Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). 27 Manx comets were found from 2013 to 2017.

 there are 4584 known comets. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is estimated to be one trillion. Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular. Particularly bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.

A comet may be discovered photographically using a wide-field telescope or visually with binoculars. However, even without access to optical equipment, it is still possible for the amateur astronomer to discover a sungrazing comet online by downloading images accumulated by some satellite observatories such as SOHO. SOHO's 2000th comet was discovered by Polish amateur astronomer Michał Kusiak on 26 December 2010 and both discoverers of Hale–Bopp used amateur equipment (although Hale was not an amateur).


The cat (Felis catus) is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of the family. A cat can either be a house cat, a farm cat, or a feral cat; the latter ranges freely and avoids human contact. Domestic cats are valued by humans for companionship and their ability to kill rodents. About 60 cat breeds are recognized by various cat registries.

The cat is similar in anatomy to the other felid species: it has a strong flexible body, quick reflexes, sharp teeth, and retractable claws adapted to killing small prey. Its night vision and sense of smell are well developed. Cat communication includes vocalizations like meowing, purring, trilling, hissing, growling, and grunting as well as cat-specific body language. A predator that is most active at dawn and dusk (crepuscular), the cat is a solitary hunter but a social species. It can hear sounds too faint or too high in frequency for human ears, such as those made by mice and other small mammals. Cats also secrete and perceive pheromones.

Female domestic cats can have kittens from spring to late autumn, with litter sizes often ranging from two to five kittens. Domestic cats are bred and shown at events as registered pedigreed cats, a hobby known as cat fancy. Population control of cats may be effected by spaying and neutering, but their proliferation and the abandonment of pets has resulted in large numbers of feral cats worldwide, contributing to the extinction of entire bird, mammal, and reptile species.

It was long thought that cat domestication began in ancient Egypt, where cats were venerated from around 3100 BC, but recent advances in archaeology and genetics have shown that their domestication occurred in Western Asia around 7500 BC.

 there were an estimated 220 million owned and 480 million stray cats in the world.  the domestic cat was the second most popular pet in the United States, with 95.6 million cats owned and around 42 million households own at least one cat. In the United Kingdom, 26% of adults have a cat with an estimated population of 10.9 million pet cats

The scientific name Felis catus was proposed by Carl Linnaeus in 1758 for a domestic cat. Felis catus domesticus was proposed by Johann Christian Polycarp Erxleben in 1777. Felis daemon proposed by Konstantin Alekseevich Satunin in 1904 was a black cat from the Transcaucasus, later identified as a domestic cat.

In 2003, the International Commission on Zoological Nomenclature ruled that the domestic cat is a distinct species, namely Felis catus.
In 2007, it was considered a subspecies, F. silvestris catus, of the European wildcat (F. silvestris) following results of phylogenetic research. In 2017, the IUCN Cat Classification Taskforce followed the recommendation of the ICZN in regarding the domestic cat as a distinct species, Felis catus.


Generally, a day is roughly the time of one rotation of the Earth (about 24 hours) or one rotation of other large astronomical objects. In everyday life, the word "day" often refers to a solar day, which is the length between two solar noons or times the Sun reaches the highest point. The word "day" may also refer to daytime, a time period when the location receives direct and indirect sunlight. On Earth, as a location passes through its day, it experiences morning, noon, afternoon, evening, and night. The effect of a day is vital to many life processes, which is called the circadian rhythm.

Days can be organized into calendars as dates, usually into months and years. Most calendars' arrangement of dates use either or both the Sun's (solar calendar) or the Moon's (lunar calendar) relative position in the sky. The start of a day is commonly accepted as roughly the time of the middle of the night or midnight, written as 0:00 or 12 am in 24- or 12-hour clock. Because the time of midnight varies between locations, time zones are set up to facilitate the use of a uniform standard time.

In specific applications, the definition of a day are slightly modified, such as in the SI day (exactly 86,400 seconds) used for computers and standards keeping, local mean time accounting of the Earth's natural fluctuation of a solar day, and stellar day and sidereal day (using the celestial sphere) used for astronomy. In some countries, a day may be set starting earlier or later via the daylight saving time, making it possible to have a 23- or 25-hour civil day.

The term comes from the Old English dæg, with its cognates such as dagur in Icelandic, Tag in German, and dag in Norwegian, Danish, Swedish and Dutch – all stemming from a Proto-Germanic root *dagaz. , day is the 205th most common word in US English, and the 210th most common in UK English.


Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. See glossary of engineering.

The term engineering is derived from the Latin ingenium, meaning "cleverness" and  ingeniare, meaning "to contrive, devise".

The American Engineers' Council for Professional Development (ECPD, the predecessor of ABET) has defined "engineering" as:
The creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under specific operating conditions; all as respects an intended function, economics of operation and safety to life and property.  (Includes Britannica article on Engineering)


French (  or  ) is a Romance language of the Indo-European family. It descended from the Vulgar Latin of the Roman Empire, as did all Romance languages. French evolved from Gallo-Romance, the Latin spoken in Gaul, and more specifically in Northern Gaul. Its closest relatives are the other langues d'oïl—languages historically spoken in northern France and in southern Belgium, which French (Francien) largely supplanted. French was also influenced by native Celtic languages of Northern Roman Gaul like Gallia Belgica and by the (Germanic) Frankish language of the post-Roman Frankish invaders. Today, owing to France's past overseas expansion, there are numerous French-based creole languages, most notably Haitian Creole. A French-speaking person or nation may be referred to as Francophone in both English and French.

French is an official language in 29 countries across multiple continents, most of which are members of the Organisation internationale de la Francophonie (OIF), the community of 84 countries which share the official use or teaching of French. French is also one of six official languages used in the United Nations. It is spoken as a first language (in descending order of the number of speakers) in France; Canada (especially in the provinces of Quebec, Ontario, and New Brunswick, as well as other Francophone regions); Belgium (Wallonia and the Brussels-Capital Region); western Switzerland (specifically the cantons forming the Romandy region); parts of Luxembourg; parts of the United States (the states of Louisiana, Maine, New Hampshire and Vermont); Monaco; the Aosta Valley region of Italy; and various communities elsewhere.

In 2015, approximately 40% of the francophone population (including L2 and partial speakers) lived in Europe, 36% in sub-Saharan Africa and the Indian Ocean, 15% in North Africa and the Middle East, 8% in the Americas, and 1% in Asia and Oceania. French is the second most widely spoken mother tongue in the European Union. Of Europeans who speak other languages natively, approximately one-fifth are able to speak French as a second language. French is the second most taught foreign language in the EU. All institutions of the EU use French as a working language along with English and German; in certain institutions, French is the sole working language (e.g. at the Court of Justice of the European Union). French is also the 18th most natively spoken language in the world, fifth most spoken language by total number of speakers and the second or third most studied language worldwide (with about 120 million learners as of 2017). As a result of French and Belgian colonialism from the 16th century onward, French was introduced to new territories in the Americas, Africa and Asia. Most second-language speakers reside in Francophone Africa, in particular Gabon, Algeria, Morocco, Tunisia, Mauritius, Senegal and Ivory Coast.

French is estimated to have about 76 million native speakers; about 235 million daily, fluent speakers; and another 77–110 million secondary speakers who speak it as a second language to varying degrees of proficiency, mainly in Africa. According to the OIF, approximately 321 million people worldwide are "able to speak the language", without specifying the criteria for this estimation or whom it encompasses. According to a demographic projection led by the Université Laval and the Réseau Démographie de l'Agence universitaire de la Francophonie, the total number of French speakers will reach approximately 500 million in 2025 and 650 million by 2050. OIF estimates 700 million by 2050, 80% of whom will be in Africa.

French has a long history as an international language of literature and scientific standards and is a primary or second language of many international organisations including the United Nations, the European Union, the North Atlantic Treaty Organization, the World Trade Organization, the International Olympic Committee, and the International Committee of the Red Cross. In 2011, Bloomberg Businessweek ranked French the third most useful language for business, after English and Standard Mandarin Chinese.

The majority of French words derive from Vulgar Latin or were constructed from Latin or Greek roots. In many cases, a single etymological root appears in French in a "popular" or native form, inherited from Vulgar Latin, and a learned form, borrowed later from Classical Latin. The following pairs consist of a native noun and a learned adjective:
 brother: frère / fraternel from Latin frater / fraternalis
 finger: doigt / digital from Latin digitus / digitalis
 faith: foi / fidèle from Latin fides / fidelis
 eye: œil / oculaire from Latin oculus / ocularis

However, a historical tendency to Gallicise Latin roots can be identified, whereas English conversely leans towards a more direct incorporation of the Latin:
 rayonnement / radiation from Latin radiatio
 éteindre / extinguish from Latin exstinguere
 noyau / nucleus from Latin nucleus
 ensoleillement / insolation from Latin insolatio

There are also noun-noun and adjective-adjective pairs:
 thing/cause: chose / cause from Latin causa
 cold: froid / frigide from Latin frigidum

It can be difficult to identify the Latin source of native French words because in the evolution from Vulgar Latin, unstressed syllables were severely reduced and the remaining vowels and consonants underwent significant modifications.

More recently the linguistic policy of the French language academies of France and Quebec has been to provide French equivalents to (mainly English) imported words, either by using existing vocabulary, extending its meaning or deriving a new word according to French morphological rules. The result is often two (or more) co-existing terms for describing the same phenomenon.
 mercatique / marketing
 finance fantôme / shadow banking
 bloc-notes / notepad
 ailière / wingsuit
 tiers-lieu / coworking

It is estimated that 12% (4,200) of common French words found in a typical dictionary such as the Petit Larousse or Micro-Robert Plus (35,000 words) are of foreign origin (where Greek and Latin learned words are not seen as foreign). About 25% (1,054) of these foreign words come from English and are fairly recent borrowings. The others are some 707 words from Italian, 550 from ancient Germanic languages, 481 from other Gallo-Romance languages, 215 from Arabic, 164 from German, 160 from Celtic languages, 159 from Spanish, 153 from Dutch, 112 from Persian and Sanskrit, 101 from Native American languages, 89 from other Asian languages, 56 from other Afro-Asiatic languages, 55 from Balto-Slavic languages, 10 from Basque and 144 (about 3%) from other languages.

One study analyzing the degree of differentiation of Romance languages in comparison to Latin estimated that among the languages analyzed French has the greatest distance from Latin. Lexical similarity is 89% with Italian, 80% with Sardinian, 78% with Rhaeto-Romance, and 75% with Romanian, Spanish and Portuguese.


The history of film chronicles the development of a visual art form created using film technologies that began in the late 19th century.

Although the advent of film as an artistic medium is not clearly defined, the commercial, public screening of ten of the Lumière brothers' short films in Paris on 28 December 1895 can be regarded as the breakthrough of projected cinematographic motion pictures. There had been earlier cinematographic results and screenings by others like the Skladanowsky brothers, who used their self-made Bioscop to display the first moving picture show to a paying audience on 1 November 1895 in Berlin, but they lacked either the quality, financial backing, stamina or the luck to find the momentum that propelled the cinématographe Lumière into a worldwide success.

Soon film production companies and studios were established all over the world. The first decade of motion picture saw film moving from a novelty to an established mass entertainment industry. The earliest films were in black and white, under a minute long, without recorded sound and consisted of a single shot from a steady camera.

Conventions toward a general cinematic language developed over the years with editing, camera movements and other cinematic techniques contributing specific roles in the narrative of films.

Special effects became a feature in movies since the late 1890s, popularized by Georges Méliès' fantasy films. Many effects were impossible or impractical to perform in theater plays and thus added more magic to the experience of movies.

Technical improvements added length (reaching 60 minutes for a feature film in 1906), synchronized sound recording (mainstream since the end of the 1920s), color (mainstream since the 1930s) and 3D (temporarily popular in the early 1950s and mainstream since the 2000s). Sound ended the necessity of interruptions of title cards, revolutionized the narrative possibilities for filmmakers, and became an integral part of moviemaking.

Popular new media, including television (mainstream since the 1950s), home video (mainstream since the 1980s), and internet (mainstream since the 1990s) influenced the distribution and consumption of films. Film production usually responded with content to fit the new media, and with technical innovations (including widescreen (mainstream since the 1950s), 3D and 4D film) and more spectacular films to keep theatrical screenings attractive.

Systems that were cheaper and more easily handled (including 8mm film, video and smartphone cameras) allowed for an increasing number of people to create films of varying qualities, for any purpose (including home movies and video art). The technical quality was usually lower than that of professional movies, but improved with digital video and affordable high quality digital cameras.

Improving over time, digital production methods became more and more popular during the 1990s, resulting in increasingly realistic visual effects and popular feature-length computer animations.

Different film genres emerged and enjoyed variable degrees of success over time, with huge differences among, for instance, horror films (mainstream since the 1890s), newsreels (prevalent in U.S. cinemas between the 1910s and the late 1960s), musicals (mainstream since the late 1920s) and pornographic films (experiencing a Golden Age during the 1970s).

During the 1980s, audiences began increasingly watching films on their home VCRs. In the early part of that decade, the film studios tried legal action to ban home ownership of VCRs as a violation of copyright, which proved unsuccessful. Eventually, the sale and rental of films on home video became a significant "second venue" for exhibition of films, and an additional source of revenue for the film industries. Direct-to-video (niche) markets usually offered lower quality, cheap productions that were not deemed very suitable for the general audiences of television and theatrical releases.

The Lucas–Spielberg combine would dominate "Hollywood" cinema for much of the 1980s, and lead to much imitation. Two follow-ups to Star Wars, three to Jaws, and three Indiana Jones films helped to make sequels of successful films more of an expectation than ever before. Lucas also launched THX Ltd, a division of Lucasfilm in 1982, while Spielberg enjoyed one of the decade's greatest successes in E.T. the Extra-Terrestrial the same year. 1982 also saw the release of Disney's Tron which was one of the first films from a major studio to use computer graphics extensively. American independent cinema struggled more during the decade, although Martin Scorsese's Raging Bull (1980), After Hours (1985), and The King of Comedy (1983) helped to establish him as one of the most critically acclaimed American film makers of the era. Also during 1983 Scarface was released, which was very profitable and resulted in even greater fame for its leading actor Al Pacino. Probably the most successful film commercially was Tim Burton's 1989 version of Bob Kane's creation, Batman, which broke box-office records. Jack Nicholson's portrayal of the demented Joker earned him a total of $60,000,000 after figuring in his percentage of the gross.

British cinema was given a boost during the early 1980s by the arrival of David Puttnam's company Goldcrest Films. The films Chariots of Fire, Gandhi, The Killing Fields and A Room with a View appealed to a "middlebrow" audience which was increasingly being ignored by the major Hollywood studios. While the films of the 1970s had helped to define modern blockbuster motion pictures, the way "Hollywood" released its films would now change. Films, for the most part, would premiere in a wider number of theatres, although, to this day, some films still premiere using the route of the limited/roadshow release system. Against some expectations, the rise of the multiplex cinema did not allow less mainstream films to be shown, but simply allowed the major blockbusters to be given an even greater number of screenings. However, films that had been overlooked in cinemas were increasingly being given a second chance on home video.

During the 1980s, Japanese cinema experienced a revival, largely due to the success of anime films. At the beginning of the 1980s, Space Battleship Yamato (1973) and Mobile Suit Gundam (1979), both of which were unsuccessful as television series, were remade as films and became hugely successful in Japan. In particular, Mobile Suit Gundam sparked the Gundam franchise of Real Robot mecha anime. The success of Macross: Do You Remember Love? also sparked a Macross franchise of mecha anime. This was also the decade when Studio Ghibli was founded. The studio produced Hayao Miyazaki's first fantasy films, Nausicaä of the Valley of the Wind (1984) and Castle in the Sky (1986), as well as Isao Takahata's Grave of the Fireflies (1988), all of which were very successful in Japan and received worldwide critical acclaim. Original video animation (OVA) films also began during this decade; the most influential of these early OVA films was Noboru Ishiguro's cyberpunk film Megazone 23 (1985). The most famous anime film of this decade was Katsuhiro Otomo's cyberpunk film Akira (1988), which although initially unsuccessful at Japanese theaters, went on to become an international success.

Hong Kong action cinema, which was in a state of decline due to endless Bruceploitation films after the death of Bruce Lee, also experienced a revival in the 1980s, largely due to the reinvention of the action film genre by Jackie Chan. He had previously combined the comedy film and martial arts film genres successfully in the 1978 films Snake in the Eagle's Shadow and Drunken Master. The next step he took was in combining this comedy martial arts genre with a new emphasis on elaborate and highly dangerous stunts, reminiscent of the silent film era. The first film in this new style of action cinema was Project A (1983), which saw the formation of the Jackie Chan Stunt Team as well as the "Three Brothers" (Chan, Sammo Hung and Yuen Biao). The film added elaborate, dangerous stunts to the fights and slapstick humor, and became a huge success throughout the Far East. As a result, Chan continued this trend with martial arts action films containing even more elaborate and dangerous stunts, including Wheels on Meals (1984), Police Story (1985), Armour of God (1986), Project A Part II (1987), Police Story 2 (1988), and Dragons Forever (1988). Other new trends which began in the 1980s were the "girls with guns" subgenre, for which Michelle Yeoh gained fame; and especially the "heroic bloodshed" genre, revolving around Triads, largely pioneered by John Woo and for which Chow Yun-fat became famous. These Hong Kong action trends were later adopted by many Hollywood action films in the 1990s and 2000s.

In Indian cinema, another star actor, considered by many to be the most natural actor in Indian cinema, Mohanlal acted in his first movie. During the 80's he rose to become a super star in Indian cinema. Indian cinema as a whole was changing in a new wave of movies and directors.


Feminism is a range of socio-political movements and ideologies that aim to define and establish the political, economic, personal, and social equality of the sexes. Feminism incorporates the position that society prioritizes the male point of view and that women are treated unjustly in these societies. Efforts to change this include fighting against gender stereotypes and establishing educational, professional, and interpersonal opportunities and outcomes for women that are equal to those for men.

Feminist movements have campaigned and continue to campaign for women's rights, including the right to vote, run for public office, work, earn equal pay, own property, receive education, enter contracts, have equal rights within marriage, and maternity leave. Feminists have also worked to ensure access to contraception, legal abortions, and social integration and to protect women and girls from rape, sexual harassment, and domestic violence. Changes in female dress standards and acceptable physical activities for females have often been part of feminist movements.

Some scholars consider feminist campaigns to be a main force behind major historical societal changes for women's rights, particularly in the West, where they are near-universally credited with achieving women's suffrage, gender-neutral language, reproductive rights for women (including access to contraceptives and abortion), and the right to enter into contracts and own property. Although feminist advocacy is, and has been, mainly focused on women's rights, some feminists argue for the inclusion of men's liberation within its aims, because they believe that men are also harmed by traditional gender roles. Feminist theory, which emerged from feminist movements, aims to understand the nature of gender inequality by examining women's social roles and lived experience; feminist theorists have developed theories in a variety of disciplines in order to respond to issues concerning gender.

Numerous feminist movements and ideologies have developed over the years and represent different viewpoints and aims. Traditionally, since the 19th century, first-wave liberal feminism that sought political and legal equality through reforms within a liberal democratic framework was contrasted with labour-based proletarian women's movements that over time developed into socialist and Marxist feminism based on class struggle theory. Since the 1960s, both of these traditions are also contrasted with radical feminism that arose from the radical wing of second-wave feminism and that calls for a radical reordering of society to eliminate male supremacy; together liberal, socialist and radical feminism are sometimes called the "Big Three" schools of feminist thought.

Since the late 20th century, many newer forms of feminisms have emerged. Some forms of feminism have been criticized for taking into account only white, middle class, college-educated, heterosexual, or cisgender perspectives. These criticisms have led to the creation of ethnically specific or multicultural forms of feminism, such as black feminism and intersectional feminism. Some feminists have argued that feminism often promotes misandry and the elevation of women's interests above men's, and criticize radical feminist positions as harmful to both men and women.

According to 2014 Ipsos poll covering 15 developed countries, 53 percent of respondents identified as feminists, and 87 percent agreed that "women should be treated equally to men in all areas based on their competency, not their gender". However, only 55 percent of women agreed that they have "full equality with men and the freedom to reach their full dreams and aspirations". Taken together, these studies reflect the importance differentiating between claiming a "feminist identity" and holding "feminist attitudes or beliefs".

According to a 2015 poll, 18 percent of Americans use the label of "feminist" to describe themselves, while 85 percent are feminists in practice as they reported they believe in "equality for women". The poll found that 52 percent did not identify as feminist, 26 percent were unsure, and 4 percent provided no response.

Sociological research shows that, in the US, increased educational attainment is associated with greater support for feminist issues. In addition, politically liberal people are more likely to support feminist ideals compared to those who are conservative.

According to numerous polls, 7 percent of Britons use the label of "feminist" to describe themselves.


Feminist views on sexuality vary, and have differed by historical period and by cultural context. Feminist attitudes to female sexuality have taken a few different directions. Matters such as the sex industry, sexual representation in the media, and issues regarding consent to sex under conditions of male dominance have been particularly controversial among feminists. This debate has culminated in the late 1970s and the 1980s, in what came to be known as the feminist sex wars, which pitted anti-pornography feminism against sex-positive feminism, and parts of the feminist movement were deeply divided by these debates. Feminists have taken a variety of positions on different aspects of the sexual revolution from the 1960s and 70s. Over the course of the 1970s, a large number of influential women accepted lesbian and bisexual women as part of feminism.


Gold is a chemical element with the symbol Au (from ) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal in a pure form. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).

Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), forming a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid alone, which dissolves silver and base metals, a property long used to refine gold and confirm the presence of gold in metallic substances, giving rise to the term 'acid test'. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold also dissolves in mercury, forming amalgam alloys, and as the gold acts simply as a solute, this is not a chemical reaction.

A relatively rare element, gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy. Gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after the Nixon shock measures of 1971.

In 2020, the world's largest gold producer was China, followed by Russia and Australia. A total of around 201,296 tonnes of gold exists above ground, . This is equal to a cube with each side measuring roughly . The world consumption of new gold produced is about 50% in jewelry, 40% in investments and 10% in industry. Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to its continued use in corrosion-resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, production of colored glass, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine.

Pure metallic (elemental) gold is non-toxic and non-irritating when ingested and is sometimes used as a food decoration in the form of gold leaf. Metallic gold is also a component of the alcoholic drinks Goldschläger, Gold Strike, and Goldwasser. Metallic gold is approved as a food additive in the EU (E175 in the Codex Alimentarius). Although the gold ion is toxic, the acceptance of metallic gold as a food additive is due to its relative chemical inertness, and resistance to being corroded or transformed into soluble salts (gold compounds) by any known chemical process which would be encountered in the human body.

Soluble compounds (gold salts) such as gold chloride are toxic to the liver and kidneys. Common cyanide salts of gold such as potassium gold cyanide, used in gold electroplating, are toxic by virtue of both their cyanide and gold content. There are rare cases of lethal gold poisoning from potassium gold cyanide. Gold toxicity can be ameliorated with chelation therapy with an agent such as dimercaprol.

Gold metal was voted Allergen of the Year in 2001 by the American Contact Dermatitis Society; gold contact allergies affect mostly women. Despite this, gold is a relatively non-potent contact allergen, in comparison with metals like nickel.

A sample of the fungus Aspergillus niger was found growing from gold mining solution; and was found to contain cyano metal complexes, such as gold, silver, copper, iron and zinc. The fungus also plays a role in the solubilization of heavy metal sulfides.


The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )) is a trans-boundary river of Asia which flows through India and Bangladesh. The  river rises in the western Himalayas in the Indian state of Uttarakhand. It flows south and east through the Gangetic plain of North India, receiving the right-bank tributary, the Yamuna, which also rises in the western Indian Himalayas, and several left-bank tributaries from Nepal that account for the bulk of its flow. In West Bengal state, India, a feeder canal taking off from its right bank diverts 50% of its flow southwards, artificially connecting it to the Hooghly river.  The Ganges continues into Bangladesh, its name changing to the Padma. It is then joined by the Jamuna, the lower stream of the Brahmaputra, and eventually the Meghna, forming the major estuary of the Ganges Delta, and emptying into the Bay of Bengal. The Ganges-Brahmaputra-Meghna system is the third largest river on earth by discharge.

The main stem of the Ganges begins at the town of Devprayag, at the confluence of the Alaknanda, which is the source stream in hydrology on account of its greater length, and the Bhagirathi, which is considered the source stream in Hindu mythology.

The Ganges is a lifeline to millions of people who live in its basin and depend on it for their daily needs. It has been important historically, with many former provincial or imperial capitals such as Pataliputra, Kannauj, Kara, Munger, Kashi, Patna, Hajipur, Delhi, Bhagalpur, Murshidabad, Baharampur, Kampilya, and Kolkata located on its banks or the banks of tributaries and connected waterways. The river is home to approximately 140 species of fish, 90 species of amphibians, and also reptiles and mammals, including critically endangered species such as the gharial and South Asian river dolphin. The Ganges is the most sacred river to Hindus. It is worshipped as the goddess Ganga in Hinduism.

The Ganges is threatened by severe pollution. This poses a danger not only to humans but also to animals. The levels of fecal coliform bacteria from human waste in the river near Varanasi are more than a hundred times the Indian government's official limit. The Ganga Action Plan, an environmental initiative to clean up the river, has been considered a failure which is variously attributed to corruption, a lack of will in the government, poor technical expertise, environmental planning and a lack of support from  religious authorities.

The Indian subcontinent lies atop the Indian tectonic plate, a minor plate within the Indo-Australian Plate. Its defining geological processes commenced seventy-five million years ago, when, as a part of the southern supercontinent Gondwana, it began a northeastwards drift—lasting fifty million years—across the then unformed Indian Ocean. The subcontinent's subsequent collision with the Eurasian Plate and subduction under it, gave rise to the Himalayas, the planet's highest mountain ranges. In the former seabed immediately south of the emerging Himalayas, plate movement created a vast trough, which, having gradually been filled with sediment borne by the Indus and its tributaries and the Ganges and its tributaries, now forms the Indo-Gangetic Plain.

The Indo-Gangetic Plain is geologically known as a foredeep or foreland basin.


In linguistics, the grammar of a natural language is its set of structural constraints on speakers' or writers' composition of clauses, phrases, and words. The term can also refer to the study of such constraints, a field that includes domains such as phonology, morphology, and syntax, often complemented by phonetics, semantics, and pragmatics. There are currently two different approaches to the study of grammar: traditional grammar and theoretical grammar.

Fluent speakers of a language variety or lect have effectively internalized these constraints, the vast majority of which – at least in the case of one's native language(s) – are acquired not by conscious study or instruction but by hearing other speakers. Much of this internalization occurs during early childhood; learning a language later in life usually involves more explicit instruction. In this view, grammar is understood as the cognitive information underlying a specific instance of language production.

The term "grammar" can also describe the linguistic behavior of groups of speakers and writers rather than individuals. Differences in scales are important to this sense of the word: for example, the term "English grammar" could refer to the whole of English grammar (that is, to the grammar of all the speakers of the language), in which case the term encompasses a great deal of variation. At a smaller scale, it may refer only to what is shared among the grammars of all or most English speakers (such as subject–verb–object word order in simple declarative sentences). At the smallest scale, this sense of "grammar" can describe the conventions of just one relatively well-defined form of English (such as standard English for a region).

A description, study, or analysis of such rules may also be referred to as grammar. A reference book describing the grammar of a language is called a "reference grammar" or simply "a grammar" (see History of English grammars). A fully explicit grammar, which exhaustively describes the grammatical constructions of a particular speech variety, is called descriptive grammar. This kind of linguistic description contrasts with linguistic prescription, an attempt to actively discourage or suppress some grammatical constructions while codifying and promoting others, either in an absolute sense or about a standard variety. For example, some prescriptivists maintain that sentences in English should not end with prepositions, a prohibition that has been traced to John Dryden (13 April 1668 – January 1688) whose unexplained objection to the practice perhaps led other English speakers to avoid the construction and discourage its use. Yet preposition stranding has a long history in Germanic languages like English, where it is so widespread as to be a standard usage.

Outside linguistics, the term grammar is often used in a rather different sense. It may be used more broadly to include conventions of spelling and punctuation, which linguists would not typically consider as part of grammar but rather as part of orthography, the conventions used for writing a language. It may also be used more narrowly to refer to a set of prescriptive norms only, excluding those aspects of a language's grammar which are not subject to variation or debate on their normative acceptability. Jeremy Butterfield claimed that, for non-linguists, "Grammar is often a generic way of referring to any aspect of English that people object to."

Prescriptive grammar is taught in primary and secondary school. The term "grammar school" historically referred to a school (attached to a cathedral or monastery) that teaches Latin grammar to future priests and monks. It originally referred to a school that taught students how to read, scan, interpret, and declaim Greek and Latin poets (including Homer, Virgil, Euripides, and others). These should not be mistaken for the related, albeit distinct, modern British grammar schools.

A standard language is a dialect that is promoted above other dialects in writing, education, and, broadly speaking, in the public sphere; it contrasts with vernacular dialects, which may be the objects of study in academic, descriptive linguistics but which are rarely taught prescriptively. The standardized "first language" taught in primary education may be subject to political controversy because it may sometimes establish a standard defining nationality or ethnicity.

Recently, efforts have begun to update grammar instruction in primary and secondary education. The main focus has been to prevent the use of outdated prescriptive rules in favor of setting norms based on earlier descriptive research and to change perceptions about the relative "correctness" of prescribed standard forms in comparison to non-standard dialects. A series of metastudies have found that the explicit teaching of grammatical parts of speech and syntax has little or no effect on the improvement of student writing quality in elementary school, middle school of high school; other methods of writing instruction had far greater positive effect, including strategy instruction, collaborative writing, summary writing, process instruction, sentence combining and inquiry projects.

The preeminence of Parisian French has reigned largely unchallenged throughout the history of modern French literature. Standard Italian is based on the speech of Florence rather than the capital because of its influence on early literature. Likewise, standard Spanish is not based on the speech of Madrid but on that of educated speakers from more northern areas such as Castile and León (see Gramática de la lengua castellana). In Argentina and Uruguay the Spanish standard is based on the local dialects of Buenos Aires and Montevideo (Rioplatense Spanish). Portuguese has, for now, two official standards, respectively Brazilian Portuguese and European Portuguese.

The Serbian variant of Serbo-Croatian is likewise divided; Serbia and the Republika Srpska of Bosnia and Herzegovina use their own distinct normative subvarieties, with differences in yat reflexes. The existence and codification of a distinct Montenegrin standard is a matter of controversy, some treat Montenegrin as a separate standard lect, and some think that it should be considered another form of Serbian.

Norwegian has two standards, Bokmål and Nynorsk, the choice between which is subject to controversy: Each Norwegian municipality can either declare one as its official language or it can remain "language neutral". Nynorsk is backed by 27 percent of municipalities. The main language used in primary schools, chosen by referendum within the local school district, normally follows the official language of its municipality. Standard German emerged from the standardized chancellery use of High German in the 16th and 17th centuries. Until about 1800, it was almost exclusively a written language, but now it is so widely spoken that most of the former German dialects are nearly extinct.

Standard Chinese has official status as the standard spoken form of the Chinese language in the People's Republic of China (PRC), the Republic of China (ROC), and the Republic of Singapore. Pronunciation of Standard Chinese is based on the local accent of Mandarin Chinese from Luanping, Chengde in Hebei Province near Beijing, while grammar and syntax are based on modern vernacular written Chinese.

Modern Standard Arabic is directly based on Classical Arabic, the language of the Qur'an. The Hindustani language has two standards, Hindi and Urdu.

In the United States, the Society for the Promotion of Good Grammar designated 4 March as National Grammar Day in 2008.


The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age (Paleolithic, Mesolithic, Neolithic) and the Bronze Age (Chalcolithic). The concept has been mostly applied to Iron Age Europe and the Ancient Near East, but also, by analogy, to other parts of the Old World.

The duration of the Iron Age varies depending on the region under consideration. It is defined by archaeological convention. The "Iron Age" begins locally when the production of iron or steel has advanced to the point where iron tools and weapons replace their bronze equivalents in common use. In the Ancient Near East, this transition took place in the wake of the so-called Bronze Age collapse, in the 12th century BCE. The technology soon spread throughout the Mediterranean Basin region and to South Asia (Iron Age in India) between the 12th and 11th century BCE. Its further spread to Central Asia, Eastern Europe, and Central Europe is somewhat delayed, and Northern Europe was not reached until around the start of the 5th century BCE.

The Iron Age is taken to end, also by convention, with the beginning of the historiographical record.
This usually does not represent a clear break in the archaeological record; for the Ancient Near East, the establishment of the Achaemenid Empire c. 550 BCE is traditionally and still usually taken as a cut-off date, later dates being considered historical by virtue of the record by Herodotus, despite considerable written records from far earlier (well back into the Bronze Age) now being known. In Central and Western Europe, the Roman conquests of the 1st century BC serve as marking for the end of the Iron Age. The Germanic Iron Age of Scandinavia is taken to end c. AD 800, with the beginning of the Viking Age.

In the Indian sub-continent, the Iron Age is taken to begin with the ironworking Painted Gray Ware culture. Recent estimates suggest that it ranges from the 15th century BCE, through to the reign of Ashoka in the 3rd century BCE. The use of the term "Iron Age" in the archaeology of South, East, and Southeast Asia is more recent and less common than for Western Eurasia. In China, written history started before iron-working arrived, so the term is infrequently used. The Sahel (Sudan region) and Sub-Saharan Africa are outside of the three-age system, there being no Bronze Age, but the term "Iron Age" is sometimes used in reference to early cultures practicing ironworking, such as the Nok culture of Nigeria.

The three-age system was introduced in the first half of the 19th century for the archaeology of Europe in particular, and by the later 19th century expanded to the archaeology of the Ancient Near East. Its name harks back to the mythological "Ages of Man" of Hesiod. As an archaeological era, it was first introduced for Scandinavia by Christian Jürgensen Thomsen in the 1830s. By the 1860s, it was embraced as a useful division of the "earliest history of mankind" in general and began to be applied in Assyriology. The development of the now-conventional periodization in the archaeology of the Ancient Near East was developed in the 1920s to 1930s.
As its name suggests, Iron Age technology is characterized by the production of tools and weaponry by ferrous metallurgy (ironworking), more specifically from carbon steel.


The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.

Nearly all organisms have some kind of immune system. Bacteria have a rudimentary immune system in the form of enzymes that protect against virus infections. Other basic immune mechanisms evolved in ancient plants and animals and remain in their modern descendants. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system. Jawed vertebrates, including humans, have even more sophisticated defense mechanisms, including the ability to adapt to recognize pathogens more efficiently. Adaptive (or acquired) immunity creates an immunological memory leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired immunity is the basis of vaccination.

Dysfunction of the immune system can cause autoimmune diseases, inflammatory diseases and cancer. Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. In humans, immunodeficiency can be the result of a genetic disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS, or the use of immunosuppressive medication. Autoimmunity results from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, and systemic lupus erythematosus. Immunology covers the study of all aspects of the immune system.

Several barriers protect organisms from infection, including mechanical, chemical, and biological barriers. The waxy cuticle of most leaves, the exoskeleton of insects, the shells and membranes of externally deposited eggs, and skin are examples of mechanical barriers that are the first line of defense against infection. Organisms cannot be completely sealed from their environments, so systems act to protect body openings such as the lungs, intestines, and the genitourinary tract. In the lungs, coughing and sneezing mechanically eject pathogens and other irritants from the respiratory tract. The flushing action of tears and urine also mechanically expels pathogens, while mucus secreted by the respiratory and gastrointestinal tract serves to trap and entangle microorganisms.

Chemical barriers also protect against infection. The skin and respiratory tract secrete antimicrobial peptides such as the β-defensins. Enzymes such as lysozyme and phospholipase A2 in saliva, tears, and breast milk are also antibacterials. Vaginal secretions serve as a chemical barrier following menarche, when they become slightly acidic, while semen contains defensins and zinc to kill pathogens. In the stomach, gastric acid serves as a chemical defense against ingested pathogens.

Within the genitourinary and gastrointestinal tracts, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space and, in some cases, changing the conditions in their environment, such as pH or available iron. As a result, the probability that pathogens will reach sufficient numbers to cause illness is reduced.


A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a virtual space, or both. A library's collection can include printed materials and other physical resources in many formats such as DVD, CD and cassette as well as access to information, music or other content held on bibliographic databases.

A library, which may vary widely in size, may be organized for use and maintained by a public body such as a government; an institution such as a school or museum; a corporation; or a private individual. In addition to providing materials, libraries also provide the services of librarians who are trained and experts at finding, selecting, circulating and organizing information and at interpreting information needs, navigating and analyzing very large amounts of information with a variety of resources.

Library buildings often provide quiet areas for studying, as well as common areas for group study and collaboration, and may provide public facilities for access to their electronic resources; for instance: computers and access to the Internet. The library's clientele and services offered vary depending on its type: users of a public library have different needs from those of a special library or academic library, for example. Libraries may also be community hubs, where programs are delivered and people engage in lifelong learning. Modern libraries extend their services beyond the physical walls of a building by providing material accessible by electronic means, including from home via the Internet.

The services the library offers are variously described as library services, information services, or the combination "library and information services", although different institutions and sources define such terminology differently.

The term library is based on the Latin word  for 'book' or 'document', contained in Latin  'collection of books' and  'container for books'. Other modern languages use derivations from Ancient Greek  (), originally meaning 'book container', via Latin  (cf. French  or German ).


Latin (,  or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the Roman Republic it became the dominant language in the Italian region and subsequently throughout the Roman Empire. Even after the fall of Western Rome, Latin remained the common language of international communication, science, scholarship and academia in Europe until well into the 18th century, when other regional vernaculars (including its own descendants, the Romance languages) supplanted it in common academic and political usage, and it eventually became a dead language in the modern linguistic definition.

Latin is a highly inflected language, with three distinct genders, six or seven noun cases, five declensions, four verb conjugations, six tenses, three persons, three moods, two voices, two or three aspects, and two numbers. The Latin alphabet is directly derived from the Etruscan and Greek alphabets.

By the late Roman Republic (75 BC), Old Latin had been standardised into Classical Latin used by educated elites. Vulgar Latin was the colloquial form spoken at that time among lower-class commoners and attested in inscriptions and the works of comic playwrights Plautus and Terence and author Petronius. Late Latin is the written language from the 3rd century and its various Vulgar Latin dialects developed in the 6th to 9th centuries into the modern Romance languages. Medieval Latin was used during the Middle Ages as a literary language from the 9th century to the Renaissance, which then used Renaissance Latin. Later, New Latin evolved during the early modern era to eventually become various forms of rarely spoken Contemporary Latin, one of which, Ecclesiastical Latin, remains the official language of the Holy See and the Roman Rite of the Catholic Church at Vatican City.

Latin has also greatly influenced the English language and historically contributed many words to the English lexicon after the Christianization of Anglo-Saxons and the Norman conquest. In particular, Latin (and Ancient Greek) roots are still used in English descriptions of theology, science disciplines (especially anatomy and taxonomy), medicine, and law.

Latin is a synthetic, fusional language in the terminology of linguistic typology. In more traditional terminology, it is an inflected language, but typologists are apt to say "inflecting". Words include an objective semantic element and markers specifying the grammatical use of the word. The fusion of root meaning and markers produces very compact sentence elements: , "I love," is produced from a semantic element, , "love," to which , a first person singular marker, is suffixed.

The grammatical function can be changed by changing the markers: the word is "inflected" to express different grammatical functions, but the semantic element usually does not change. (Inflection uses affixing and infixing. Affixing is prefixing and suffixing. Latin inflections are never prefixed.)

For example, , "he (or she or it) will love", is formed from the same stem, , to which a future tense marker, , is suffixed, and a third person singular marker, , is suffixed. There is an inherent ambiguity:  may denote more than one grammatical category: masculine, feminine, or neuter gender. A major task in understanding Latin phrases and clauses is to clarify such ambiguities by an analysis of context. All natural languages contain ambiguities of one sort or another.

The inflections express gender, number, and case in adjectives, nouns, and pronouns, a process called declension. Markers are also attached to fixed stems of verbs, to denote person, number, tense, voice, mood, and aspect, a process called conjugation. Some words are uninflected and undergo neither process, such as adverbs, prepositions, and interjections.