Quote

2.3 Module Path

Perl searches three different locations for modules, referred to in this document as core in which modules distributed with Perl are installed, vendor for packaged modules and site for modules installed by the local administrator.

The module search path (@INC) in the Debian packages has been ordered to include these locations in the following order:

site (current)

Modules installed by the local administrator for the current version of Perl (see Locally Installed Modules, Chapter 3).
/usr/local/lib/perl/version
/usr/local/share/perl/version

Where version indicates the current Perl version ($Config{version}[1]).

vendor

Packaged modules (see Packaged Modules, Chapter 4).
/usr/lib/perl5
/usr/share/perl5

core

Modules included in the core Perl distribution.
/usr/lib/perl/version
/usr/share/perl/version

site (old)

site directories (as above) for modules installed with previously released perl packages for which the current package is binary compatible are included if present.

In each of the directory pairs above, the lib component is for binary (XS) modules, and share for architecture-independent (pure-perl) modules.