Crackfic, also known as crack-fic or crack!fic, is a story intended to push the boundaries of canonical reality. It might involve bizarre pairings, out-of-this-world plots, oddball crossovers, or even merely pure nonsense. As the name suggests, crackfics are stories that make the reader say 'Was this person on drugs when they wrote this?!'
Just as with any type of fanfiction, crackfic may be good or bad. Some badfic authors will attempt to account for their less-than-stellar work by excusing it as crackfic and saying it wasn't meant to be taken seriously. Particularly bad trollfics may stray into crackfic territory.