Okay, I can’t help too much here cause that word is one of two words I don’t even fully understand here, but I’ll just post a bunch of different definitions of the word and then just tell you what I get from the word here.
Okay, so what I gathered from this is that is’a basically a ship someone has that isn’t confirmed in the fandom outlet yet(like the author hasn’t stated it, the producers of the show/movie didn’t say it in the show/movie or in any interviews), but you believe the ship to be true. Headcanon’s usually differ from each person with not many people believing in the same headcanon. The second definition from fuckyeahroleplayadvice and the last definition from zoniis what helped me out. I’ll try to give a few examples of my interpretation of the word.
In The Vampire Diaries, Matt and Bonnie have been pretty close friends. She saved his life after he drowns himself to get info from Vicki last season and this season they won Prom King and Queen. Matt hasn’t had any love interests since Caroline in season 2, and Bonnie’s been grieving over the death of her ex boyfriend who she still had feelings for, Jeremy. With all of this is in play, no one has come out and said the ship is a reality. They don’t even really have scenes together alone either except for her saving his life and the prom stuff. Usually, they are accompanied by Elena, Caroline, or someone else in their little clique. While Rebekah did question Matt on his relationship with Bonnie in the Prom episode Pictures of You, that’s the furthest anyone on the show has gotten to hinting that Monnie/Batt is a ship. Therefore, one could believe them to be a headcanon. They would be a more popular headcanon.
Other examples from The Vampire Diaries would be Tyler and Elena and Jeremy and Katherine.
I was going to try to do a Glee one, but here’s this lovely tag filled with glee headcanons.
Okay so my examples may be totally off but that’s what I got from the term. I hope the definitions above helped you out a bit. Honestly, answering this question helped me out with the term so thanks for asking it and I hoped it helped.
EDIT: I learned what this word means! Like really learned what it means. I wasn’t totally off base. A headcanon is basically something you believe to be true about a character that hasn’t been confirmed by the writers/author/etc. It can be a ship, but it can also be a hobby they have, or past experiences in their life. To further explain this, I’ll give you a really short and simple sample bio and then headcanon’s someone can draw from it.
Bio: Jane is a vampire. She was turned in the 1900s after her maker witnessed her depression and thought turning her would make her life better. It did. During the Roaring Twenties Jane became the life of the party. She got herself involved in the bootlegging business and was almost always on the guest list for any party of importance. She even fell in love with a man named Alexander. However, near the end of the decade, she came back to her home to discover Alexander dead. She spent the next few decades mourning over the loss of her love. However, through the aid of some new friends and some positive events in her life, she has managed to pull her life back together. She’s living life to the fullest again.
So that bio just sucked, I know, but here are what some examples of headcanon’s one could pull out of that bio.
Do you guys get that? I just pulled those three headcanon’s out of that bio because that’s the vibe I was getting from it. I felt as if Jane would of been a part of those things. Even though it wasn’t stated in the bio as canon, those three points are still my own headanon’s I’ll incorporate with the character when roleplaying them. And yeah. I hope this helps!