Retroactive Continuity (RetCon or retcon for short) is the changing of a story aspect from what was previously stated as canonical. The term can be in reference to a remake of an original piece in which changes are made, or to a complete and utter butchering of the original canon. Tara often retcons in the beginning of her story, when introducing characters from the original canon as massively changed characters. Go ahead. Click on all of those links. I dare you.