Short name pragma, long name pragmatic module.

These are modules which change the behaviour of the Perl interpreter. For example:
use integer;
change arithmetic operations, (division and the like) so the results are integers. e.g.

print 5 / 2;
use integer;
print 5 / 2;

will print 2.5 and then 2.

And there are the two paragmatic modules you should always use, until you feel confident with Perl:

use warnings;
use strict;

These two pragmas will help you find your logic errors and dubious constructs.

Unlike normal modules, pragmatic modules last until the closing parenthesis (or more acurately, until the end of the enclosing scope). Or you can explicitely revoke them with

no integer;

See Programming Perl page 136, and chapter 31.