Headcannon 

A personal belief or interpretation about a story or pice of media that has not been confirmed nor denied in the media itself.

It’s my headcannon that they eventually make it back home, but we’ll never know because the series ended with them attempting to escape.

Headcannon by Hellohihey February 9, 2020

headcannon 

A miniature cannon mounted on one’s head. Used mainly to prank unsuspecting friends. A headcannon is very difficult to ignore.

“I’ve got a new headcannon.”
“Yeah?”
“Yeah.”
*launches cannonball at friend*

headcannon by coyotedomino March 2, 2018

Headcannon 

A Headcannon is a story (or really anything) that is added on to or changed in a persons mind. For example, in Undertale, someone may make up a story on how Papyrus joined the Royal guard, since this doesn't happen in-game, this makes it someone's headcannon. Headcannons usually aren't shared, but you can find headcannons of many things on many different social platforms.

Person 1: "That doesn't happen in the story."
Person 2: I know, its my personal headcannon.

Headcannon by Withered Rose April 10, 2022

handcannon 

huge pistol of some sort I.E. .44 mag, .454 casull, .50AE, .500 S&W

guy #1: check this piece out

guy#2: holy shit that things a fucking handcannon!!

handcannon by carlbittner March 26, 2009

headcanon

Used by followers of various media of entertainment, such as television shows, movies, books, etc. to note a particular belief which has not been used in the universe of whatever program or story they follow, but seems to make sense to that particular individual, and as such is adopted as a sort of "personal canon". Headcanon may be upgraded to canon if it is incorporated into the program or story's universe.

In my headcanon, John and Mary bicker like siblings when they're around each other... They just seem like they're brother and sister to me!

headcanon by the-deudliest-firearm July 17, 2012

Headcanon

(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 media consumer themselves or the fandom in general. If it is confirmed by the creator of the story, it becomes canon.

In Homestuck , a popular webcomic , many suspect the headcanon that the trolls are carnivores, because of their natural homicidal tendencies and sharp teeth. It's never explicitly stated in the comic that this is true, but it'd be kind of dumb to assume they're a race known for salads and ice cream sundaes.

Headcanon by TickTockTimeTraveler October 12, 2014

Headcanon

Now... reality can be whatever I want...
-Thanos

person 1: omg i headcanon todoroki and dek-
person 2: please stfu

Headcanon by ._.daydreaming April 11, 2022