My understanding is that the term was invented by Mr Heller for his famous and wonderful book. He originally called it CATCH-18, but Leon Uris published a book called MILA 18 that same year, and there was concern that readers would be confused, so the number was changed.
A “catch” is indeed a snag, a hook, a con, a sting, a trick. If you hear of an offer that sounds to good to be true, you ask “What’s the catch?”
In the novel, the use of a high number (22) implies that there is some standard list of such snags, which is a nice humourous touch IMHO.
The essence of Catch-22 is that you’re damned if you do and damned if you don’t, in a circular way. The examples from the book abound:
- The only way to get out of flying bombing missions is if you’re crazy, but if you’re trying to get out of bombing missions, that’s perfectly reasonable behaviour, so you’re not crazy.
- Major Major goes into his office through the door (to be “in the office”) and then immediately sneaks out the back window (so he’s not in the office); hence, the secretary says that the only time he’s in the office is when he’s out.
… and so on.