A function is not necessarily a computing term -- in the English language it could mean anything from something your body does to a social event. A subroutine, however, is pretty much limited to a computing term, although i'm sure someone has used it outside of that scope. (UPDATE: touché, ysth!) In Perl, i tend to refer to the built-in functions such as print and sort as functions, but i refer to my own functions as subroutines. Of interest is perldoc -f, which is used to pull up documentation for Perl's built-in subroutines [sic]. ;) Notice it is -f and not -s.

As diotalevi said, they are homonyms in terms of computing.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)