ACC: Adaptive Cruise Control - Works just like a conventional cruise control system - until it detects a car in front of it. Sensors detect that you are approaching a car ahead.
The system then automatically eases off the throttle or even gently applies the brakes to maintain a constant safe distance (which you can adjust) behind that vehicle. As soon as the vehicle pulls into another lane, ACC accelerates, smoothly and progressively, to your original chosen speed.