4WD have low gearing in the transfer case, AWD does not. 4WD can be full time or part time, meaning it can or cannot be driving on dry pavement without causing binding and excessive driveline wear, respectively. The 4th gen 4Runner left in 4-Hi is the same as AWD, but since it has 4-Lo, it's a full time 4WD since it also has a center differential.