[short for ‘retroactive continuity’, from the Usenet newsgroup rec.arts.comics]
1. n. The common situation in pulp fiction (esp. comics or soap operas) where a new story ‘reveals’ things about events in previous stories, usually leaving the ‘facts’ the same (thus preserving continuity) while completely changing their interpretation. For example, revealing that a whole season of Dallas was a dream was a retcon.
2. vt. To write such a story about a character or fictitious object. “Byrne has retconned Superman's cape so that it is no longer unbreakable.” “Marvelman's old adventures were retconned into synthetic dreams.” “Swamp Thing was retconned from a transformed person into a sentient vegetable.”
[This term is included because it is a good example of hackish linguistic innovation in a field completely unrelated to computers. The word retcon will probably spread through comics fandom and lose its association with hackerdom within a couple of years; for the record, it started here. —ESR]
[1993 update: some comics fans on the net now claim that retcon was independently in use in comics fandom before rec.arts.comics, and have citations from around 1981. In lexicography, nothing is ever simple. —ESR]