The differential for different wheel speeds of driven axles.
Different wheel speeds occur when cornering because one wheel of an axle a longer path than the other.
Speed compensation of the driven axles in most cases taken care of by a bevel gear differential.
A limited-slip differential directs power to the wheel with the better traction and the other wheel from spinning freely.
The differential is on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles.
These all-wheel-drive vehicles need a differential between each set of drive wheels, and they need one between the front and the back wheels as well, because the front wheels a different distance through a turn than the rear wheels.