meaning that it is 'of the story' or something that could/did ACTUALLY happen in a story, used by fans and fanfictioners
Izzi: Gosh, Marrie, you really like the Harry and Ginny pairing for Harry Potter...
Marrie: Yeah, but it's totally cannon.
Izzi: I know, I read the seventh book
Jen: OMG! McGee and Abby are such a cute couple.
Dan: And it's cannon, have you seen the latest NCIS episode?
Jen: I know, Abby totally kissed McGee's head!!
An artillery piece, or something of that nature. I'm only writing this because I'm perturbed that the top definition for "cannon" is a misspelling of "canon." Are people really that stupid? I believe the answer is yes.
A Person that is a very funny person, a rare name given by some, and those who possess it, will be remembered by all. A all in all nice guy, powns at games, and a greatlover to all women.
Jeffrey: dang i wish my name was cannon, mine is soo plain and original.