What do anti-lock braking systems prevent when used in an emergancy stopping situation?

Answer 1

They will prevent brake lock up and a skid.
ABS would stop the wheels from locking up. Generally if the brakes are pressed hard (without ABS), the tires will lock preventing you from getting any friction on low friction surfaces and making it difficult to drive on any surface. In ice or rain, ABS are especially useful.
Anti-lock breaks are designed to prevent wheels from skidding, or lossing traction in the case of an emergency stop.
It prevents the tires from locking up.
Anti-lock brake systems prevent the car tires from locking and skidding. Once a skid starts, it becomes more difficult to stop the vehicle. Also, skids can cause the car to move sideways into other cars.

Answer 2

Exactly what their name implies - the prevent the brakes from locking up.

Answer 3

It prevents the wheels from locking up.

Answer 4

Skidding due to locking up of the wheels.