I don't know, but both Gemini and Wikipedia in my primary language seem to agree that AWD refers to 4WD with a center decoupling mechanism to run front and back in an asynchronous manner, with emphasis on Wikipedia only that this is strictly American definition of it and both describe both style of systems in the rest of the world.

I'm guessing that maybe a distinction between offroad capable cars and non-capable cars is useful for liability reasons. Or something else.

I don't think most people here have it right. From my understanding the main difference is that 4WD can be manually turned off (meaning going to 2WD mode). AWD is always on.

Some AWD systems might intelligently change power to different wheels (or front and back) and that might vary per brand and model. 4WD could also do this. Usually with 4WD you might also have a 4 lo and 4 hi gear as well.

Then there's also various types of differentials and locks and whatnot which is a whole more detailed discussion.

AWD is an automatic 4 wheel drive when required.

Think of it more like it's going to be 2WD most of the time, but when there is low traction (such as ice) the 4WD will engage as power is always going to all wheels.

4WD is a permanent thing, or at least always on when you engage it. The system locks all the wheels to the same spin speed.

AWD is for on-road use. Each tire rotates at its own speed.

4WD is for off-road use. All tires rotate at the same speed.

Clutch pack vs transfer case.