A Project Object Model or POM is the fundamental unit of work in
Maven. It is an XML file that contains information about the project
and configuration details used by Maven to build the project. It
contains default values for most projects. Examples for this is the
build directory, which is target; the source directory, which is
src/main/java; the test source directory, which is src/main/test; and
so on.The POM was renamed from project.xml in Maven 1 to pom.xml in Maven 2.
Instead of having a maven.xml file that contains the goals that can be
executed, the goals or plugins are now configured in the pom.xml. When
executing a task or goal, Maven looks for the POM in the current
directory. It reads the POM, gets the needed configuration
information, then executes the goal.
Source: Official Documentation