An unusual relationship of any kind of fandom (i.e. books, television shows, movies, ect.) that is unlikely to happen. In fact a person must be on crack to even support such a relationship.

A relationship that is so insane, it must be on crack. Relatively common in fan fiction.

Crack ship, crack!ship, or crack pairing is a term often used in fan fiction or role playing that pairs two people pairing from different fandom universes into a romantic relationship. This can be anything from a tv show, video game, or a book. A crack ship usually makes the readers question "Why such an off pairing" Some people might like it, some hate it, and others might be grossed out.

A relationship between two characters from different fandoms (tv shows, films, books etc), that is impossible to achieve.

A friendship or relationship formed between crackheads soley because cracks attract, and enjoy doing cracktivities together.