Canonical
Canonical--an adjective derived from canon--essentially means "standard" or "generally accepted" or "part of the backstory." It is used by theologians and canon lawyers to refer to the canons of the Eastern Orthodox and Roman Cathlolic churches, adopted by ecumenical councils.
It also means "part of the canon", i.e., one of the books composing the Bible, as opposed to apocryphal books. It is used most often when describing bodies of literature (see Canon (fiction)), or as a popular term in computing jargon (where it has the same basic meaning).
For a good article on the word's use among computer types, see the Jargon File's entry for the word.
