What does **/* mean in maven syntax?

It is more related to Ant convention upon which Maven is built.
**/* : all files in all subdirectories: see Ant Patterns.

When ** is used as the name of a directory in the pattern, it matches zero or more directories.
For example: /test/** matches all files/directories under /test/, such as /test/x.java, or /test/foo/bar/xyz.html, but not /xyz.xml.

 http://stackoverflow.com/questions/905845/what-does-mean-in-maven-syntax