Fanon

Fanon 

Refers to common plot or character elements that were not established by the original source material, but are generally accepted to be true by the fans anyway. These are the un-official details, folks. Fanon concepts have often become so prevalent in the fandom that their origins (which fan came up with the idea first) are no longer remembered. Example: In The Sentinel fandom, the minor canon character of Detective Rafe was never given a first name. Fanon, however, assigned him the name of Brian and it stuck.