How do you call a certain book file that explains a world?

[Robin]

so yeah.

If I had a book/file that explained every detail of a world (be it real or imaginative). What would that be called?

It isn't a lexicon and I don't want to call it a 'summary'
EDIT:

I don't want to call it an encyclopedia either, it is more a file for an author that first writes down his world and all of its rules and laws and all of that. I want a fancy name for it if possible