Skiing is a way of traveling over snow, using skis strapped to one's feet. In modern times it has been mostly an athletic activity. Skis are used in conjunction with boots that connect to the ski with use of a binding. Commonly, ski poles or "stocks" are used to improve balance and timing as well as for propulsion. Skiing can be grouped into two general categories: Nordic and Alpine. Nordic skiing, the older of the two disciplines, originated in Scandinavia and uses free-heel bindings that attach at the toes of the skier's boots but not at the heels.