hi this drives me crazy
canon is what happens in the text. e.g. merlin tries to poison morgana
a headcanon is a fact that you have personally made up as an elaboration of canon. it is your invention. e.g. i think morgana and gwen had a teenage lesbian situationship before the events of canon. or, i think modern morgana would love evanesence.
an interpretation is how one reads the existing text. it is not an invented fact nor is it a headcanon, it is a reading. e.g. i think merlin tries to poison morgana out of misplaced self-hatred. or, i think that one line was delivered with suppressed malice and shows a nuanced relationship.
fanon is the general fandomās accepted headcanons and interpretations that elaborate or recontextualize canon. e.g. merlin is a badass waif and morgana is a bitch.
these are all different words with different meanings.
and a cannon is a large mounted gun, usually on wheels, that uses explosives to fire projectiles.
