"Femslash" seems to have some currency as the lesbian equivalent of "slash". I've also seen "slash" used to refer to both types of gay relationships. I've also seen it used to refer to sexual content (straight or gay), and sometimes specifically to gay sexual content (to the point where some people say PG-rated fic with gay couples is not slash - in particular there's a tripartite division with "gen", "het", and "slash", where the first has no sex, the second has straight sex, and the third has gay sex). I don't think non-canonicity is part of any definition I've seen.

It may be just me, but I get the impression that it's not really slash if the characters in question are gay in canon, even if not for each other. I might argue that, say, Ben Bruckner / Melanie Marcus (both canon!gay, opposite sexes) would count as slash, but I expect that's a minority position.