See the current Perl documentation for lib:subs.

Here is our local, out-dated (pre-5.6) version:

subs - Perl pragma to predeclare sub names

    use subs qw(frob);
    frob 3..10;

This will predeclare all the subroutine whose names are in the list, allowing you to use them without parentheses even before they're declared.

Unlike pragmas that affect the $^H hints variable, the use vars and use subs declarations are not BLOCK-scoped. They are thus effective for the entire file in which they appear. You may not rescind such declarations with no vars or no subs.

See perlmodlib and strict.