Sidecut
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.
Read more about Sidecut.