Ski mountaineering (abbreviated to skimo) is a skiing discipline that involves climbing mountains either on skis or carrying them, depending on the steepness of the ascent, and then descending on skis. There are two major categories of equipment used, free-heel Telemark skis and skis based on Alpine skis, where the heel is free for ascents, but is fixed during descent. The discipline may be practiced recreationally or as a competitive sport.