Canon
Also known as Headcanon · Fanon · Retcon
Canon is the official material that counts as part of a fictional world, and so decides what “really happened” in it.
The books themselves are always canon. The edges are where people argue: novellas and short stories, deleted scenes, something the author said on social media, a TV adaptation that changes the ending. Every fandom draws the line in a slightly different place, and adaptations usually get treated as their own separate canon.
You’ll hear three related terms a lot. Headcanon is your own personal belief about a character or event that the books don’t confirm or rule out. Fanon is a headcanon so widespread that people start remembering it as canon. A retcon is when a later book changes something earlier books had established. Sometimes that’s a fix, and sometimes it’s a contradiction nobody accepts.
These arguments get heated because canon decides what’s actually in a world a lot of people share. If you’ve spent years with a character, hearing that part of their story has been rewritten can feel like a big deal.
Canon: common questions
What is the difference between canon and headcanon?
Canon is what the official material says happened. Headcanon is your own interpretation that the books don’t confirm. It might be plausible, but nobody else has to agree with it.
What is a retcon?
Short for retroactive continuity. It’s when a later work changes something earlier canon had established, either to fix a mistake or to take the story in a new direction.