Cross-country skiing is travel on skis over snow-covered terrain, whereby skiers rely on their own locomotion rather than on ski lifts or other forms of assistance. Modern cross-country skiing shares self-locomotion as a core attribute with the original form of skiing from which all skiing disciplines evolved, including alpine skiing, ski jumping and Telemark skiing. It is widely practised as a sport and recreational activity, however some still use it as a means of transportation. Variants of cross-country skiing are adapted to a range of terrain which spans unimproved, sometimes mountainous terrain to groomed courses that are specifically designed for the sport. Skiers propel themselves either by striding forward (classic style) or side-to-side in a skating motion (skate skiing), aided by arms pushing on ski poles against the snow. It is practised in regions with snow-covered landscapes, including Northern Europe, Canada, Russia and regions in the United States. Competitive cross-country skiing is one of the Nordic skiing sports. Cross-country skiing and rifle marksmanship are the two components of biathlon, ski-orienteering is a form of cross-country skiing, which includes map navigation along snow trails and tracks.