A retcon is any plot point or detail that was not intended from the beginning, but treated as if it always had been. Internal Retcon · Cosmic Retcon · Cerebus Retcon · Orwellian Retcon

Often (especially lately), Cosmic Retconning is the go-to method for demolishing Continuity Lock-Out and drawing in a younger audience. As a rule of thumb, ...

An explicit retcon occurred in the season 9 episode "The Principal and the Pauper", where it was revealed that Seymour Skinner is actually an impostor, ...

When a Retcon is performed by going back and changing the original work, so that subsequent printings of "the same" work are actually different.

The Cerebus Retcon gives a rational, often cynical, In-Universe explanation or interpretation of early gags, frequently by giving them a late Deconstruction.

Most popular as a way of ending either a story arc or a story proper. Naturally, spoilers are rather unavoidable in describing this phenomenon as a result.

The Metal Gear series tends to have each new installment retcon at least one more-or-less significant plot detail from the previous game.

A parody retcon is when a creator, in response to negative critical reaction to their work, handwaves the work's failings by claiming that it was supposed to be ...

A particular type of Retcon that focuses on taking an existing antagonistic figure and altering (potentially quite drastically) the heinousness of their crimes ...

If a Retcon is changing the past, and a Cosmic Retcon is an in-universe changing of the past, then Retconjuration is the ability to create a Cosmic Retcon.