See the current Perl documentation for pop.
Here is our local, out-dated (pre-5.6) version:
pop - remove the last element from an array and return it
Pops and returns the last value of the array, shortening the array by 1. Has a similar effect to
$tmp = $ARRAY[$#ARRAY--];
If there are no elements in the array, returns the undefined value. If
ARRAY is omitted, pops the
@ARGV array in the main program, and the
@_ array in subroutines, just like shift().