Ok, this is more of two questions, but still…

I believe a crackfic is a kind of comedy or spoof of a story or book or film. Where fanfics are just in the world of another story, crackfics are comedic versions. That is the just I got but I could be mistaken.

Crackfic is where the writer takes something that isn't believable in some manner and tries to make it believable. The best known crackfics do fall under comedy and spoofs, but these aren't the best representation of the genre. Crack fic involves pairing two unlikely people together, working with a crack theory or some other thing that people would think you are out of your mind to do. It gets its name from the fact you wouldn't think people would come up with these ideas unless they were on a sugar high, but other times they are very well thought out.