As used by most current manufacturers/advertisers, AWD (all wheel drive) has a rather different meaning and purpose than 4WD.
Currently common AWD vehicles do apply torque to all four wheels, but the purpose is NOT to provide you the ability to get across rugged terrain. The AWD feature improves handling, and especially side-slip stability on ordinary "good" road surfaces, but is not intended to be used "off-road."
In most of the more-or-less "passenger vehicles" the coupling between front and rear axles is through a fluid coupling that applies a small fraction of the drive torque (typically around 15 - 20%) to the secondary axle, with the remainder going to the "primary drive axle."
There generally is no "lockup" or anti-slip differential between the two axles, and the majority of the "consumer class" AWD vehicles do not have anti-slip or lockup differentials on either axle, so any one wheel that lacks traction does all the spinning, and torque to the remaining wheels drops to (near) zero.
(A side feature is that setting the parking brake when you jack up many AWD vehicles to change a tire does not prevent the vehicle from rolling off the jack. WHEEL CHOCKS MUST BE USED AT ALL FOUR WHEELS to safely take one wheel off the ground. VOEE1)
AWD is sort of a "first step" in a group of "stability enhancements," some of which are beginning to appear in more exotic forms. A couple of newer vehicles feature "levellers" to pump up selected shock absorber struts to apply load differentially to the corner of the vehicle that tends "lift" on curves to inhibit that wheel from "breaking loose." At least one has added a "stability braking" control that applies the brake on one or more wheels when accelerometers sense side loads indicating you're going around a curve. There are several others. ALL OF THESE "enhancements" are intended to improve handling on "improved road surfaces" and NONE are intended to significantly enhance your ability to operate "off-road" or in serious bad weather such as snow and ice.
I can attest to the usefulness of AWD. I found it a significant help on Interstate highways in rain, where the water settles into the "wear tracks" and crossing or driving in the tracks requires a lot of attention to "incipient hydroplaning." It's probably most useful on vehicles with large "longitudinal moment of inertia" - i.e. small trucks or (in my case) a fairly heavy passenger van; but it probably would provide somewhat less stressful driving in smaller vehicles.
A vehicle intended for off-road or heavy snow should be called a 4WD (assuming it has two axles). It can be a "full time 4WD" or "selectable" but it's a different animal than is intended when the term AWD is used. To be useful, a 4WD must have at least "limited slip" differentials on both axles, and preferably should have a "locked up" or limited-slip differential connection between the axles - neither of which is likely to be found in vehicles labelled as AWD.
1 VOEE = voice of embarrasing (almost) experience.