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. Construction 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). Maintenance 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. Ratings 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. North America, Australia and New Zealand 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, the direction of the fall line, and whether the trail is groomed