If I may quote from an Iron Man blog post I made last June:

In the last couple weeks, I've seen Perl questions on at least two separate forums which revolved around the connection between .pm files and Perl packages. Really, though, this connection is quite easy to understand if you just remember one thing:

It doesn't exist.

Assigning the same name to a package and to the .pm file where that package resides is purely a matter of convention, adhered to for the sake of (human) readability. It is completely ignored by the language. If you want to put package Foo into Bar.pm and use it along with a package Bar which is split between Xyzzy.pm and Quux.pm, then you're perfectly free to do so. You'll confuse the hell out of yourself and whatever poor soul is condemned to maintain your code following the inevitable collapse of your sanity, but you can do it.