Yep, I agree with the comments already made. Basically a crossover is where two fandom universes collide, and a fusion is where characters from Universe A are written in Universe B as if they'd always been there.
The other thing that often distinguishes them is that with a crossover you will have characters from both universes in the story, but with a fusion it may just be the characters from Universe A in Universe B. You don't have to have any of the Universe B characters in there. I don't think that's obligatory, but it's a very common type. (So in a Mag7/Firefly fusion, the characters from Firefly could be the Magnificant 7 rather than Chris, Vin, Ezra et al.)
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carisma_sensei
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Date: 2013-07-07 10:12 am (UTC)The other thing that often distinguishes them is that with a crossover you will have characters from both universes in the story, but with a fusion it may just be the characters from Universe A in Universe B. You don't have to have any of the Universe B characters in there. I don't think that's obligatory, but it's a very common type. (So in a Mag7/Firefly fusion, the characters from Firefly could be the Magnificant 7 rather than Chris, Vin, Ezra et al.)