See the current Perl documentation for chop.
Here is our local, out-dated (pre-5.6) version:

chop - remove the last character from a string

chop VARIABLE
chop LIST
chop

Chops off the last character of a string and returns the character chopped.
It's used primarily to remove the newline from the end of an input record,
but is much more efficient than s/\n// because it neither scans nor copies the string. If
VARIABLE is omitted, chops $_. Example:
while (<>) {
chop; # avoid \n on last field
@array = split(/:/);
#...
}
You can actually chop anything that's an lvalue, including an assignment:
chop($cwd = `pwd`);
chop($answer = <STDIN>);
If you chop a list, each element is chopped. Only the value of the last chop() is returned.
Note that chop() returns the last character. To return all but the last character, use substr($string, 0, -1).