That kind of notation is often used while discussing various fan fictions to avoid confusion when people are talking about 'canon' version of character and 'mod

That kind of notation is often used while discussing various fan fictions to avoid confusion when people are talking about 'canon' version of character and 'modified'. So it's common to just always prepend which version you're talking about, so HPMOR!Harry/canon!Harry/other-fan-fic!Voldemort etc. etc.