Retcon

Retroactive continuity — commonly refered to as retcon — is the adding of new information to "historical" material, or deliberately changing previously established facts in a work. The change itself is referred to as a "retcon", and the act of writing and publishing a retcon is called "retconning".

Retcons are common in comic books, especially those of large publishing houses such as Marvel Comics, because of the lengthy history of many series and the number of independent authors contributing to their development; this is the context in which the term was coined.