there are 4 wheels ....and they are all driven by an axle. They are a drive wheel, there for having four of them, it's AWD. The differential is what allows them to spin at different speeds. When put in a situation where a wheel has less traction, it's an open end and this is where it has a disadvantage. LSD's come into play in situations like this and vary in allowed wheel slippage to locked diffs/spools.
A LSD also allows differential in left to right wheel speeds but having resistance to spin freely. Tightly packed clutch LSD, more resistance to speed difference and more when you apply engine torque to it as long as the wheels are on the ground.