You may also see a vendor/lib directory which holds modules written by a third party. It looks like you have ActivePerl installed: it's possible you might get one of those using PPM to install a non-ActiveState module.
I have one with my Strawberry Perl installation:
C:\_\tmp>perl -V
...
@INC:
C:/strawberry/perl/site/lib
C:/strawberry/perl/vendor/lib
C:/strawberry/perl/lib
You may come across other variations such as this from my Cygwin installation (which uses site_perl instead of site):
$ perl -V
...
@INC:
/usr/local/lib/perl5/site_perl/5.12.0/cygwin-thread-multi-64int
/usr/local/lib/perl5/site_perl/5.12.0
/usr/local/lib/perl5/5.12.0/cygwin-thread-multi-64int
/usr/local/lib/perl5/5.12.0
|