A differential is a type of simple planetary gear that consists of a drive shaft as the input and two drive wheels as the outputs. The differential has the property that angular velocity of the carrier is the mean average of the angular velocities of the annular and sun gears.
There are two basic types of differentials
Epicyclic/planetary differential: This differential uses an epicyclic gearing to split and asymmetrically apportion torque between the rear and the front axles. In some vehicles, an epicyclic differential interconnects the engine, motor generators and the drive wheels. The advantage of an epicyclic differential is that it is relatively compact along the axis length (the sun gear shaft).
Spur gear differential. This differential is composed of spur gears only. It is made of two equally sized spur gears, one for each half shaft, with a gap between them. There is a rotating carrier on the same axis as the two shafts. Torque from a transmitter rotates this carrier.