ABS makes it so that the wheels of a car do not lock and slide when the driver slams on the brakes for an emergency stop. That way the car will stop more quickly due to a larger amount of friction. It does this via a network of sensors and pistons. When the sensors detect that the wheels have begun to lock, the pistons release the brakes a little until the wheel has begun to accelerate once more. Once the wheel has begun to accelerate again, the brakes are re-applied. ABS pulses the brakes in this manner to keep static friction in play rather than the weaker force of kinetic friction, thus stopping the car more quickly than it would with locked wheels. ABS also brings with it the added bonus of being able to steer while braking. Because the wheels maintain friction with the road, they are able to respond when the driver turns the wheel and the car can be turned like normal.
