Canon originally referred to (among other things) the recognised books of the Bible. In the 20th Century however the term has also been adopted in the discussion of most long-running media franchises to mean any event, character, or location within the fiction that is considered to have been "real" with respect to that fictional continuity.
In the Ghostbusters brand, as a result of several contradictory entries into the series over the yeaers due to editorial and writer choices; the Ghostbusters brand is usually viewed as a multiverse. Due to this multiversal nature Ghostbusters canon is both extremely complicated and extremely simple, depending on how you look at it.
General canon rules
When dealing with Ghostbusters canon the following should be remember:
- All officially-licensed fiction is canonical for some continuity.
- If conflicting events occur which are ostensibly within the same continuity, there is no single "correct" interpretation, unless an official retcon is later issued. Fans may reach a consensus on it, or not at which point it becomes fanon. The two events may be relegated to slightly different continuities, or an in-continuity fix may be applied.
- While canon from one continuity cannot, in general, be used as evidence to support canon in a different continuity, there are exceptions.
- Fan fiction is not canon.
- Descriptions in toy catalogs are not canon.
- Some fans have their own ideas about what constitutes canon and nothing anyone else says will change their mind. This is called "Personal Canon"