Four-wheel drive (4WD)
A proper four-wheel drive system is what you'll get in a Land Rover, Land Cruiser, or Jeep. You can manually put it in a two-wheel drive mode (2H) that operates just like RWD. Or you can put it in what’s called 4H, which in addition to being a popular high school club in rural areas, is meant for street driving, and means all the wheels are operating a little differently from each other -- much like AWD.
But what differentiates it from AWD is a separate mode known as 4L, or four low. In this mode, all four wheels are locked together and will spin at the same rate at all times. You don't really want to use this on the street, but if you’re stuck in very deep snow or mud, this is the best way to get out, because there’s no adjusting, just the pure pulling power of all four tires working in unison.