The sidecut is a general term for the inner curvature of a ski, snowboard, or skiboard. The sidecut depth is measured as the distance between the waist of the board and an imaginary straight line that strikes both of the contact points at the tip and tail. The sidecut radius is the radial measurement of the curve that matches the inner curvature of the ski, snowboard, or skiboard. For instance, with a radial sidecut, a circle with a particular radius will perfectly fit the curvature of the sidecut. This particular radius is the given specification from the manufacturer. However, it is not necessary that the radius be constant. Mathematical functions, such as a parabola or a clothoid, are often used to describe the curvature of a sidecut. Also, multiple radii are stitched together in a piecewise fashion as well.
Parabolic skis (skis with a pronounced parabolic sidecut) were first introduced by Elan in 1993, and since then have completely taken over the alpine skiing industry. The nature of the sidecut assists in making refined carving turns.
Different types of skis have different sidecuts. Skis with drastic sidecuts tend to make quicker sharper turns and have a smaller turn radius. For example a world cup slalom ski would have an extremely large tip (probably around 120 mm) a narrow waist (in around 60mm) and a large tail (slightly narrower than the tip). The drastic shape of this ski would allow it to make extremely quick turns (radius between 11m and 14m) without skidding. The disadvantage to a pronounced sidecut is that the ski will be less stable at high speeds, preferring short, quick turns. Also, skis with a drastic sidecut will perform poorly in moguls. Most skis have a moderate amount of sidecut. This allows reasonably fast turns (radius around 17m on most skis) while still maintaining some stability at higher speeds. Another possibility is a very slight sidecut. This is commonly found on giant slalom skis and competition level mogul skis. The straighter sidecut allows skis to make long, fast, highly stable turns (radius around 22m for giant slalom, even more for most mogul skis). In mogul skis, the narrow width, straighter sidecut, and light weight allow the ski to be maneuvered through the tight troughs in the bumps. Jumping skis are very wide and have virtually parallel sides, as the ski jumper is more concerned about maintaining a fast and straight trajectory, and not turning at all.
As powder-specific constructions are becoming more popular, some extremely unusual sidecuts are beginning to appear. For example, the K2 Pontoon's widest point is the tip. It then gradually gets narrower all the way down to the tail. Also, some skis like the Volant Spatula and Goode Scoop have a reverse sidecut. In a reverse sidecut, the tip and tail are a normal size, but the ski becomes extremely wide at the waist, giving it an ovaline shape. These constructions are thought to provide maximum floatation in extremely deep powder, but they are useless on hard snow. Most people, however, prefer traditional sidecuts, even in powder.