Skis and boards have a sidecut - a curved edge. They are wider at the tips and tails, and have a narrow waist. This is designed so that when the ski or board is tipped on edge it will form a curve. The curve grips the snnow and the ski or board rides the edge and turns. The ideal track will be a thin line in the snow, with no slippage. The carve is the neatest turn that also takes least effort to accomplish.