What’s the distinction?
I'm guessing that maybe a distinction between offroad capable cars and non-capable cars is useful for liability reasons. Or something else.
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.
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.
4WD is for off-road use. All tires rotate at the same speed.
At this point, the distinction is gone, because car bards marketing.
(AI lies)
Re: the 3 locking mechanisms comment, in typical 4WD configurations the transfer case in 4H/4L is essentially locked (which is what makes the above sum front == sum rear condition). AWD transfer cases can be more flexible there; some essentially act as a 3rd differential and result in all four wheel speeds being essentially decoupled (for better or worse, easier to get stuck) while others actively control the front/back locking with clutches or hydraulics or whatever.
The "locking mechanism" known as traction works pretty well most of the time and has the nice side effect that it only wears an easily replaceable consumable when you break it.