It's seen everywhere--romance in literature. Romance is such an important thing that it gets its own category in literature, specifically named "Romance", because it focuses around desire, love, and, well, romance.

When the original author wants to have romantic relations in their stories and novels, they add it in. There's a good chance that even you can think of a good handful of cute couples in fiction. These romances are "cannon."

I spend a lot of my time (while on the internet) on Super Smash Brothers Forums. Almost every person on those forums know the definition of "cannon". "Cannon" is the original author's rendition of their own characters, stories, etcetera. For example, the story "Little Red Riding Hood" has a wolf trying to eat Lil' Red and her Grandmother. In this story's cannon, it's physically possible for the wolf to swallow Lil' Red and the Grandmother whole. In the Mickey Mouse universe, it's cannon for dogs to be pets (Pluto) and also to act as normal people (Goofy). It's clear that the original author has a say in what's what in their own universes. Another form of cannon is commonly found in video games (Hence my reference to the Super Smash Brothers forums). Let's use Mario's cannon as an example. Super Mario 64, Super Mario Sunshine, and Super Mario Galaxy are all cannon. They are additions to the story. Non-cannon games, or spin-offs, are games like Mario Kart, Mario Golf, Super Mario Strikers, etcetera. These games have nothing to do with the mainstream story.

But what happens when you interpret these characters and the relationships of the characters on your own? This is called "non-cannon", where a fan / non-author of a pre-existing universe takes the story into their own hands, and makes things like fanfictions, fancharacters, and maybe even fancomics. Some of these can be real masterpeices, while there are a good handful that fall short of what the "fanauthor" intended.

A lot of these fanfictions involve romance between characters. What happens when the fanauthor decides to say, "Huh. These characters would look cute together..." and build a story around it? Usually, it doesn't come out very well.

I most commonly see these "fanpairings" as an offense to the original creator.

Being a Sonic dork (I know not a lot of you like Sonic, just bear with me!) I've seen multiple crimes on this. I'm going to use some Sonic characters as examples, so bear with me if you really don't know what I'm talking about in the next paragraph.

A popular fanparing I see in ShadowxAmy. With all the games I've played, the most SEGA ever hinted these two to have any feeling for each other was in Sonic Adventure 2, simply when Amy mistook Shadow for being her "one true love", Sonic. The other example was Amy simply reminding Shadow of Maria. Yet, with such little cannon evidence of the two ever feeling any emotions for each other, it's an incredibly popular fanpairing.

While doing some more research (browsing art) on fanfictions and fanart, I've stumbled upon many, many, accounts of someone making a fancharacter (A character made by a fan to be put into a pre-existing universe) and having a character that has been already made to fall in love with this character.

I personally also feel this is an offense to the original artist.

I used to have my fancharacter become the girlfriend of a cannon character. It worked out great, the relationship was realistic, the setup was nice, I didn't see any flaws. There still aren't any flaws with the relationship, it's pretty bullet proof.

But the thing is--these aren't your characters. You don't choose what types of relationships they are in. It took me a long time to realize this, but once I did, I found the quality in my fanfictions to greatly increase. There's nothing wrong with fancharacters, as long as they don't interfere with the cannon in a severe way. (Like a pirate in PotC that can use a light saber. That's not cannon at all.)

Cannon is described as the author's rendition of their own made-up characters, plots, and relationships. They choose the characters to have certain relations for a reason. Nintendo chose Link and Zelda to have a thing for each other. J.K. Rowling choose Ron Weasly and Hermine Granger to (Book 7 spoilers) get married in 10 years. Spongebob and Patrick are best friends, as Nickelodeon intends.

I would be greatly offended if I saw one of my original character getting hooked up with one of your characters, or another character in my stories' cannon.

So please, respect the author, keep (At least) relationships cannon.