Format
A fictional universe can be contained in a single work, as in George Orwell's Nineteen Eighty-Four or Aldous Huxley's Brave New World, or in serialized, series-based, open-ended or round robin-style fiction.
In most small-scale fictional universes, general properties and timeline events fit into a consistently organized continuity. However, in the case of universes that are rewritten or revised by different writers, editors or producers, this continuity may be violated, by accident or by design—film productions are notorious for altering fictional canon of written series.
The occasional publishing use of retroactive continuity (retcon) often occurs due to this kind of revision or oversight. Members of fandom often create a kind of fan-made canon (fanon) to patch up such errors; "fanon" that becomes generally accepted sometimes becomes actual canon. Other fan-made additions to a universe (fan fiction, alternative universe, pastiche, parody) are usually not considered canonical unless they get authorized.
Read more about this topic: Fictional Universe