In general, I use this word to describe my stranger plot bunnies. Some examples of crackfic, written and unwritten are:
-The Mormon missionaries knock on the door of a vampire coven in Forks, WA. WRITTEN
-Sirius Black's motorbike was an Autobot and her little brother was the flying Ford Anglia. UNWRITTEN.
-Clark Kent and Anakin Skywalker have a one-upping contest about their superpowers. WRITTEN
Currently, I'm entertaining a bit of plot crack for Wingspan. It all started with the need to write a scene in which Maeve suggests that Aislin date a fairytale creature like herself. One of the recommendations is "Find yourself a nice vampire" and the answer is "Naw, he'd say I taste like chicken."
Well, then I got around to remembering my first experience with therapy. My parents sent me to a group in Needham where young teenage girls got together and talked about the problems of being, well, a teenager. It took the edge off the problems I was having with my best friend who decided she hated me, my first boyfriend moving away just when I needed a support like him, starting a new school because things were so bad at my old one, etc. I thought that somehow, Mr. and Mrs. Byrne would find a similar group for teenagers with "special needs" like their daughter's.
Now I've got this mental image of a variety of characters and the entire thing sort of reminds me of the undead meetings in Terry Pratchett's "Reaper Man." But the character who won't leave me alone is a girl bitten by a vampire just before the vampire got killed off by a pseudo-Buffy and now she's not a full vampire, but she's no longer her normal human self. She's getting through life having to have one blood transfusion a day to curb her cravings and wears long-sleeved shirts and jeans any time the UV index in Allston, MA gets above a 5.
THere are other things, but I shouldn't be surprised that, in the book that starts out with a nude shoplifter getting deported from Canada, I have some crack.