In the automobile industry, the term "ASR" is an acronym for "anti-slip regulation." Also known as an acceleration slip regulator in some car models, the ASR button basically cuts power to the wheels when slipping is detected.
The ASR button helps with slipping or sliding due to snow, ice, sand, gravel or other, similar, road hazards. According to Volkswagen manufacturers, it is a traction control system that works by reducing the engine torque and thus keeps the wheels gripping during acceleration. In that company's line of automobiles, the ASR is active at speeds above 40 km/h, which equates to about 25 mph.