It's quite the same thing.

"Package" is the technical name for what is often called a "namespace" in other languages. It can be used as an object-oriented class, or just as a module, which is simply a bunch of definitions, usually of functions.

When talking about a module, especially a CPAN module, some kind of good order is often implied - a makefile, some documentation, a well-defined API, a test suite etc., although none of it is technically required.