It is a safety program which electronically controls the trajectory of your car when driving high speed in curves or making dangerous maneuvers to the steering wheel. The system works together with the ABS system. Doesn't save you if the speed is much too high but is really miraculous if you exceed not more then 10-20 mph the recommended speed or suddenly you try to avoid something on the road.
Basically the system actuate the brakes on some wheels and cut the gas, disregarding what pedals you push at the moment.