Perl 5 Modules are similar to Perl 4 required libraries in that they provide shared resources. However, in the case of Modules, what is being shared is more than simple subroutines, but actual objects. Modules are classes that define objects that may be accessed by other applications.
For instance, our cat class could be made into a module. And then it could be used by other perl applications.
To make a module, all we need to do is give it a .pm extension and make sure it is visible to any perl application that needs to use it. Once that is done, the module is ready to use.