Alpine skiing (or downhill skiing) is a recreational activity and sport involving sliding down snow-covered hills with long, thin skis attached to each foot.
Alpine skiing evolved from cross-country skiing when ski lift infrastructure was developed at mountain resorts to tow skiers back to the top of slopes, thus making it possible to repeatedly enjoy skiing down steep, long slopes that would be otherwise too tiring to climb up. Thus, the sport is popular wherever the combination of snow, mountain slopes, and a sufficient tourist infrastructure can be built up, including much of Europe, North America, and Japan.
The main technical challenges faced by skiiers are simply how to control the direction and speed of their descent. Typically, novice skiiers use a technique called the "snowplough" to turn and stop by pointing one or both skis inward, but more advanced skiiers use more difficult but more elegant and speedier methods. These more advanced methods are known as carving. To carve, a skier rolls their knees but keeps the upper body and hips faced down the hill, so that only the knees and feet are turned. This method is far faster and is used by downhill racers.
As skiers gain confidence, they tackle steeper, longer and more uneven slopes at higher speeds. In North America the easiest slopes are marked by green circles, and are typically fairly flat and known as bunny hills. The mid-level difficulty is that of a blue square, and are more challenging but not as much as a black diamond. A black diamond is steeper than a blue square and usually involves challenging terrain. A double black diamond is for experts only, and is very difficult to ski.
However, there is no standard for these designations, it is up to each resort owner to determine. So, for instance, a blue-square (midlevel) trail at one ski mountain may be markedly more difficult than a black-diamond (expert) trail at another mountain.
In Europe the system is based on colour alone, with the level of difficulty increasing from green to blue to red to black.
