Is there an official list of assumptions used in GAAP? According to the wikipedia, GAAP is just a bunch of very high level principles, such as be honest, consistent, give your best estimate of your finances... But it doesn't seem to prescribe any particular rules to use, just that you use them consistently. And then, what does that mean about non-GAAP ? Does non-GAAP basically allow you to be inconsistent and dishonest or use less than your best guess ?
GAAP just means the local accounting standard. So US GAAP for the USA. UK GAAP mean FRS102 etc.
Non-GAAP essentially means the company decided it's extra special and the standard accounting doesn't capture it's uniqueness. Sometimes that's true but most of the time it's executive not liking what the GAAP number tells them.
A good example is WeWork's "Community Adjusted EBITDA".
Edit: I found a little more detail under revenue recognition page on wikipedia : https://en.wikipedia.org/wiki/Revenue_recognition