I'm trying to argue (and this is a prescriptive rather than descriptive argument, because obviously people are using "slash" in all SORTS of ways) that slash is a particular kind of erotic fanfiction which definitionally involves a NONCANONICAL relationship. 9 times out of 10 this is m/m--10 times out of 10 in ordinary usage.

In other words, I think Scully/Mulder should have been labeled slash during the first 5 (?) seasons.

(I also think Scully/Mulder should have STAYED slash, but that's a very different argument.)