@MattЭллен [Headcanon](http://headcanon.urbanup.com/6331777) (also written as "head canon" but it's really one word.)
An idea, belief, or aspect of a story that is not mentioned in the media itself, but is accepted by either the reader themselves or the [\[fandom\]](http://urbandictionary.com/define.php?term=fandom) in general. If it is confirmed by the author of the story, it becomes [\[canon\]](http://urbandictionary.com/define.php?term=canon).