"Canon" is the vague continuity that the powers that be want to promote at any given time. The canon of Trek includes everything...books, comics, cartoons, etc. If it's good enough for them to put the Star Trek label on and expect people to pay for then it all counts. At any time "Canon" can be expanded or withdrawn from any of the canon materials. If it's on the screen (TV or movie) or page, it's part of Trek. If one part is contradicted by another just remember that there's an infinite number of universes out there. Episode A just occurs in a slightly different one than Movie B or Novel C.