User:Demi/Wikipedia is not a reference to fictional worlds

Wikipedia is not a reference to fictional works, though it can be a reference about them, assuming they are notable.

Fiction is a single source
Good encyclopedic coverage of a topic uses several sources. This is not possible for the information contained within a work of fiction--other "sources" can only be mere repetitions (albeit, perhaps, in another form) of the information contained within the fictional work itself. As an encyclopedia is not a primary source, nor yet a secondary source, but is mostly concerned with covering the analysis, context and explanations of others (preferably a lot of others), this makes it impossible to effectively cover subject matter that appears only within a work.

Remember, however, that the relevant measure of multiple sources is potential--just because an article is not covered by multiple sources now doesn't mean it doesn't belong.

This is intertwined with the idea of notability: much information taken from fictional works is non-notable, because it is not of interest outside its narrow constituency. This is partly due to the fact that fiction is a single source, but is also due to other notability-related ideas like verifiability and no original research.

Exceptions
Besides the fact that works of fiction (if notable) should be covered just as any other publication, there are "exceptions" where items or characters from fiction become notable in their own right and need coverage of their own. Big Brother and Skynet, for example, are referred to outside of the context of their particular milieus.

Covering fictional works
A good rule of thumb is that if a piece of information would be more useful to a resident of the fictional world described by a work than it would be to one outside of it, it is not encyclopedic. It makes sense to synopsize plots and identify main characters or events. But explanation of fictional technology, treatment of characters as biographical subjects, the construction of timelines of fictional histories, etc. are all examples of content that doesn't belong in an encyclopedia.

Fans of Sherlock Holmes sometimes play what they call "The Game," where (in their fan publications and other social interactions) they pretend that Sherlock Holmes was a real person, and the novels by Arthur Conan Doyle descriptions of real events actually written by Dr. Watson. As an encyclopedia, we can (and should) cover The Game; but not engage in it.