Clearly, the intelectual discussions of the past few years about the game's canon have yielded little to no fruit. So let's try discussing something else for a change. Say, the fandom's interpretation of the canon, their takes on it, their modifications of it, etc.
I will start this off with a very simple yet complex question:
What is an AU (alternative universe) and what is an AT (alternative timeline)? Who can the best define the meaning of these two buzzwords? Bonus points if your explanation actually agrees with their exact meaning, as in, you will be able to define what is a "timeline", what is a "universe", and what does "alternative" mean exactly.
(Though, if you do agree that they're just mere buzzwords, you can define your own terms and explain them below. My ultimate goal is to get to the bottom of fan story categorization, and why is everyone so obsessed with differentiating between "AUs" and "ATs".)
Resolved. Update:
Maybe I didn't make it clear right away, but my ultimate goal with this discussion is to get to the bottom of fan story categorization, not just deciding what AU and AT means. The aforementioned "fruitless discussions" were the past speculations about unresolved parts of the game, so similarly, I wanted this to become a discussion about something even more fanon-centered, as it is obvious by now that the prior discussions haven't come to any clear conclusion (btw, as mentioned by some, the most sensible explanation is that an AT is literally a canon, reset-induced change, so literally an "alternative timeline", whereas an AU is everything that introduces anything new not seen, mentioned or expanded upon in the game; in other words the actual meat and bone of the fandom).
So if you are just coming in to this discussion, then this is my next question:
Assuming the above, that an "AU" is anything that introduces ANY non-canon element to the original story (including even the most trivial of things, such as a mere head canon) or changes or erases ANY part of it, is it possible to categorize every AU? (Obviously, we don't have a full catalog of all the AUs, but we can certainly approximate the job from those that we do know about.)