A piste (//) is a marked ski run or path down a mountain for snow skiing, snowboarding, or other mountain sports.
This European term is French ("trail", "track") and synonymous with 'trail', 'slope', or 'run' in North America. The word is pronounced using a long "e" sound so that it rhymes with "beast".
North Americans employ its common European antonym, 'off piste', to describe backcountry skiing, especially when referring to skiing outside officially approved areas of a ski resort.
Pistes are not naturally occurring features, and must be created through human means. This can be done by "clearing" (removing the trees only) or by "grading" (clearing followed by reshaping of the surface by machines like graders). 
Pistes are usually maintained using tracked vehicles known as snowcats to compact or "groom" the snow to even out trail conditions, remove moguls, and redistribute snow to extend the ski season. Natural snow is often augmented with snow making machines and snow reserves, early in the season or when the snowpack is low, and to ensure the snow lasts throughout the season.
Typically, grading is done by the resort, and grades are relative to other trails within that resort. As such, they are not classified to an independent standard; although they are likely to be roughly similar, skiers should be cautious about assuming that grades in two different resorts are absolutely equivalent.
In North America, Australia and New Zealand, a color–shape rating system is used to indicate the comparative difficulty of trails (otherwise known as slopes or pistes).
The steepness of ski trails is usually measured by grade (as a percentage) instead of degree angle. In general, beginner slopes (green circle) are between 6% and 25%. Intermediate slopes (blue square) are between 25% and 40%. Difficult slopes (black diamond) are 40% and up. However, this is just a general "rule of thumb". Although slope gradient is the primary consideration in assigning a trail difficulty rating, other factors come into play. A trail will be rated by its most difficult part, even if the rest of the trail is easy. Ski resorts assign ratings to their own trails, rating a trail compared only with other trails at that resort. The resort may take into consideration the width of the trail, sharpest turns, terrain roughness, and whether the trail is groomed regularly.
|Trail rating||Level of difficulty||Description|
|Green circle||Easiest||The easiest slopes at a mountain. Generally, Green Circle trails are wide and groomed, with slope grades ranging from 6% to 25%|
|Intermediate difficulty slopes. Generally, Intermediate trails are groomed, with grades ranging from 25% to 40%. Blue Square trails make up the bulk of pistes at most ski areas.|
|Amongst the most difficult slopes at a mountain. Generally, Black Diamond trails are steep (40% and up) and may or may not be groomed.|
|Double black diamond||Expert Only
|These trails are even more difficult than Black Diamond, due to exceptionally steep slopes and other hazards such as narrow trails, exposure to wind, and the presence of obstacles such as steep drop-offs or trees. They are intended only for the most experienced skiers.
This trail rating is fairly new; by the 1980s, technological improvements in trail construction and maintenance, coupled with intense marketing competition, led to the creation of a Double Black Diamond rating.
|Variations||Various||Variations such as doubling a symbol to indicate increased difficulty, or combining two different symbols to indicate intermediate difficulty are occasionally used, as is often in Colorado at Winter Park resort and other Colorado ski resorts. One example is a diamond overlapping a square to indicate a trail rating between a Blue Square and a Black Diamond, colloquially a 'Blue-Black'. This is used by several eastern resorts, with notable example being at Windham, New York. Many resorts throughout Colorado use a double diamond with an "EX" in the center to mark a run with extreme terrain, even more difficult than a double diamond. Other resorts, such as Smugglers' Notch, Vermont, Le Massif, Quebec, Big Sky, Montana and Mt. Bohemia, Michigan, use triple black diamonds. The combination of symbols is comparatively rare at U.S. ski areas; most ski resorts stick to the standard 4-symbol progression (with the exception of the common EX runs in Colorado).
Non-standard symbols for standard ratings may be encountered at some ski areas. Bogus Basin, a resort near Boise, Idaho, uses orange diamonds on trailhead signs considered to be more difficult than double black diamonds; however, those trails are indicated on the trail map as double black diamonds. Jiminy Peak, MA uses two variations of normal trail ratings; one is a blue square with a green circle inside of it used to represent an easy-intermediate trail. The other is a blue square with a single black diamond in it, used to represent an intermediate-hard trail.
|Terrain parks||Various||Terrain parks are whole or portions of trails that can offer a variety of jumps, half-pipes, and other special "extreme" sporting obstacles beyond traditional moguls. The trails are typically represented by an orange rectangle with rounded corners.
Usually, the terrain park will carry its own trail rating, indicating the level of challenge. A terrain park with a Black Diamond or Double Black Diamond rating would contain greater and more challenging obstacles than a park with a Blue Square rating. Typically, a skier would be able to descend through a terrain park without necessarily negotiating any of its features, making this a possible easier way down than other options.
In Europe, pistes are classified by a color-coded system. The actual color system differs in parts for each country, although in all countries blue (easy), red (intermediate) and black (expert) are used. Shapes are often not used, sometimes all ratings are circles as being defined in the basic rules of the German Skiing Association DSV. The three basic color codes of the DSV have been integrated into the national standards DIN 32912 in Germany and ÖNORM S 4610 f in Austria.
In Scandinavia, a similar system is used with the addition of shapes, simplifying the identification of snow covered signs (see table below).
Slopes marked green, blue or red are groomed in all countries; blacks are groomed in Italy, Austria, Switzerland and Scandinavian resorts, while in France most black slopes are not groomed, but some are. All other classifications are generally not groomed. Sometimes slopes are marked on piste maps as dotted or as dashed lines, this also signifies that the slope is not groomed.
|Piste rating||Level of difficulty||Description|
|Green||Learning/beginner||France, Poland, Spain, Bulgaria, UK and other countries.|
These are usually not marked trails, but tend to be large, open, gently sloping areas at the base of the ski area or traverse paths between the main trails.
|Blue||Easy||These are almost always groomed. The slope gradient does not normally exceed 25% except for short wide sections with a higher gradient.|
|Red||Intermediate||Steeper or narrower than a blue slope, these are usually groomed, unless the narrowness of the trail prohibits it. The slope gradient does not normally exceed 40% except for short wide sections with a higher gradient.|
|Black||Advanced or expert||Steep, may or may not be groomed, or may be groomed for mogul skiing. In Austria, Italy and Switzerland black pistes are nearly always groomed, as non-groomed pistes are marked as skiroutes or itineraires (see below); in France, some black pistes are groomed, but most are not. Black can be a very wide classification, ranging from a slope marginally more difficult than a red, to very steep avalanche chutes like the infamous Couloirs of Courchevel. France tends to have a higher limit between red and black.|
|Orange||Extremely difficult||Austria, Switzerland, and certain other areas only.|
In a small number of areas, orange is used to mark pistes that are more difficult than black.
|In recent years, many areas reclassified some black slopes to yellow slopes. These are ungroomed and unpatrolled routes which are actually off-piste skiing, but marked and secured from avalanches. Famous examples are the Stockhorn area in Zermatt and the Tortin slopes in Verbier. In Austria, skiroutes are usually marked with orange squares instead. It is also common to mark these routes with a red diamond or a red diamond with black edges, the latter being more difficult.|
|Red diamond with black edges|
Alpine slope classification in Europe is less rigidly tied to slope angle than in North America. A lower angle slope may be classified as more difficult than a steeper slope if it requires better skiing ability because, for example, it is narrower, requires carrying speed through flatter sections or controlling speed through sharp hairpin turns, or features off-camber slope angles or exposed rock.
In Norway, Sweden and Finland, a system is used with similar colours as elsewhere in Europe, but with shapes as well.
|Piste rating||Level of difficulty||Description|
|Green circle||Very easy||Up to 9° (16%) slope.|
|Blue square||Easy||Up to 15° (27%) slope.|
|Red rectangle||Moderately difficult||Up to 25° (47%) slope.|
|Black diamond||Difficult||Over 25° (47%) slope. Triple black diamond may also be used in some areas.|
|Double black diamond||Very difficult|
Japan uses a color-coded system, but shapes do not usually accompany them. Some resorts, mainly those catering to foreigners, use the North American or European color-coding system, adding to the confusion. The usual ratings are:
|Piste rating||Level of difficulty||Description|
|Green||Beginner||These are usually near the base of the mountain, although some follow switchback routes down from the top.|
|Red||Intermediate||At most ski areas in Japan, these constitute the majority of the slopes.|
|Black||Expert||Expert slopes. These are the steepest and most difficult slopes at the ski area. The difficulty of these compared to like-classified slopes at other ski areas is heavily dependent on the target audience.|
Japan has more than 1000 ski areas (115 in Nagano Prefecture alone), many of them small and family-oriented, so comparisons between slope classifications in Japan and "equivalent" slopes in Europe or North America can be misleading.