ABS stands for Anti-lock Braking System. When a driver brakes hard — especially on wet, icy, or loose surfaces — the wheels can stop turning and skid. ABS rapidly pulses the brakes to stop that from happening, letting the tires keep gripping the road so the driver can still steer.
For a commercial truck, that added control shortens the odds of a jackknife or a loss of steering in an emergency stop, which is why the system is standard safety equipment on modern tractors and trailers.