A term initially from Buffy The Vampire Slayer Fanfiction, the term 'Jossed' is now used in many fandoms as a description of when a fanfiction writer's explanation of a certain event or exploration of a characters' motivations which previously is ambiguous, is then explained by the actual fandom, and contradicts the fanfiction writers story.
The term is derived from the creator of Buffy the Vampire Slayer, Joss Whedon. The term is most prevalent in the science fiction genre.
It is used most commonly when authors are led to believe that a certain event may happen later in a Television series or book and write a story with that event in it, then the official author goes in a different direction, making their story 'AU', Alternate Universe.
This story about Buffy living in Los Angeles got Jossed when Buffy returned to Sunnydale. Now it's AU.