Originally from Scandinavia, cross-country skiing, or Nordic skiing, is a form of free and ecological skiing. It is practiced on flat terrains or grounds with low or medium elevation gains, generally over long distances. It uses light equipment of long and narrow skis whose bindings keep the heel free. The ascending slopes are crossed only thanks to the physical strength of the skier, which makes it a particularly intense sport. The forms of practice vary from walking and hiking to Nordic raid through popular or competitive races.