Get a safari account on O'Reilly's and check out Perl Objects, References & Modules. I would suggest buying the book outright but the safari account lets you see if this is needed in your library before hand.

Quoting from the above:
Chapter 12 Using Modules
"A module is a building block for your program: a set of related subroutines and variables packaged so it can be reused."
That defines what you are doing.

I would also suggest these resources:

• Tutorials on writing modules
• Writing Practical Perl Modules