I would have assumed that non-canon relationships were slash, which goes to show how fringy I am.
I think slash refers especially to non-canon gay relationships, and fiction centered around or involving such relationships. (It may actually refer to gay male relationships in particular, I'm not quite sure. I only know the basics of fanfic terminology.)
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.
ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
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