Maven "Module" vs "Project" (Eclipse, m2eclipse plugin)

They are basically the same thing, but with one difference.
When you create a module, you must specify a parent project.
When you specify the parent project, it adds a <modules> section to the parent projects pom.xml.
That section basically says to the parent project:
run every command I get against all of my modules first
So for example, if you run, mvn package on the top-level project, it will run mvn package against all its module projects first.

Hope that helps.

Hint:
Make sure all modules have high cohesion and related to each other, otherwise you will have a huge messy project without applying SRP (Single Responsibility Principle)

Found it! My searches were returning tons of hits for creating a "multi-module project", but once I added "-multi" to my query, the answer was on the first page.

According to Creating and Importing Projects:

m2eclipse provides the ability to create a Maven module. Creating a Maven module is almost identical to creating a Maven project as it also creates a new Maven project using a Maven archetype. However, a Maven module is a subproject of another Maven project typically known as a parent project.