What is the perl corelist?
Every release of perl includes some commonly used modules, for example
CPAN, file system utilities like File::Spec, File::Find.
The module Module::CoreList contains a database with a list of these modules for every perl release.
Module::CoreList itself is delivered with perl since version 5.8.9, and it comes with a command line utility script corelist.
How can I use modules that are not in this list?
Distributions like ActivePerl or operating systems like Debian or RedHat
usually deliver some additional modules that are not in the corelist.
For Debian you can use the following website to check which module is included in a Debian release and in which version:
Any other module you can install with tools like cpan, cpanplus or ppm. See perlmodinstall