A retcon is basically a 'do-over' that can have varying degrees of impact on the character(s) involved or the MUX as a whole. The term is something of an abbreviation of "retroactive continuity" and is used to categorize any instance where existing continuity is changed in some way.

Continuity changes may be one of the following:

• Rewriting history to remove an event from history.
• Rewriting history to insert an event into history.

Retcons occur to varying degrees and have varied degrees of severity in terms of impact on MUX continuity.