plugins/maven-plugin/root-pom.html

<div>
  If your workspace has the top-level <code>pom.xml</code> in somewhere other
  than the 1st module's root directory, specify the path (relative to
  the module root) here, such as <code>parent/pom.xml</code>.
  <br>
  If left empty, defaults to <code>pom.xml</code>
</div>