Term used in fandom to describe something that has never been shown on screen (on the show / in the movie) and yet is generally accepted as canon by many fans. Example: It is fanon that the TV show The Magnificent Seven is set in a town called Four Corners --it was called that in the script of the pilot, but the town has never been named on air.
FANON
Meaning of FANON in English
Slang English vocab. Английский сленговый словарь. 2012