Alpine skiing is a popular winter sport that involves skiing down a mountain slope on skis. It is also known as downhill skiing and is usually done on groomed trails. Heli-skiing is a more extreme form of skiing that involves being dropped off at the top of a mountain by helicopter and skiing down the mountain. It is often done in remote areas and is considered to be a more dangerous form of skiing due to the lack of groomed trails and the potential for avalanches.