Head Canon vs Alternate Reality

runpunkrun is having a fantastically interesting conversation about terminology in fandom by age demographic.

It struck a chord with me because I keep seeing this term headcanon and two people have used it in comments to fic I posted at AO3. I find it curious because in both cases, for me, the scenarios are not head canon. They are AU's taking a left at canon. Headcanon to me (that turned into fanon after awhile, I think) is Buffy always smelling like vanilla. It's true in my head and always shall be so! Fic is so often AU which is just an alternative to the canon. Using the word canon suggests a concrete idea of what something is or should be. And AU's are explorations from a point in canon. Naming something a head canon then, for me, suggests a personal understanding of events that will not change from how I perform the intersection between the source and fandom. Like how no matter what I write about Buffy, she always smells like vanilla (even when it's mixed in with the scent of dirt or blood).

My favorite headcanon is actually a post-series canon. One Thousand Kisses Deep was a fic that I wrote about the end of the slayers and that, to me, is how the series ends. It's obviously an AU from Chosen, but if I had my way that is a narrative end that makes sense.