The fact that the foot is only attached

The Telemark ski is a downhill or touring ski, where the binding attaches only at the toe. The Telemark ski was the first ski with a significant side cut, and evolved in the Telemark region of southern Norway early in the 19th century. It was popularized by Sondre Norheim of Morgedal in Telemark, when he demonstrated the ski and the Telemark style of skiing to the public at Christiana, Norway beginning in 1868. The fact that the foot is only attached to the ski at the toes means that flexible ski boots are worn. The primary turning technique involves pushing one foot forward and lifting the heel of the other foot.

Cross-country skis are very light and narrow, and usually have slight sidecut, though some newer skis are a sidecut more like an alpine ski. The boots attach to the bindings at the toes only. Three binding systems are popular: Rottefella's NNN, Salomon's SNS profil, and SNS pilot.
The ski bases are waxed to reduce friction during forward motion, and kick wax can also be applied for adhesion when walking uphill. Some waxless models may have patterns on the bottom to increase the friction when the ski slides backward.
The two major techniques are classical (traditional striding) and freestyle or skating, which was developed in the 1980s. Skating skis are shorter than classical skis and do not need grip wax. The skating technique is used in biathlons. V1 skating is done when going up a hill and one arm is the lead arm which poles ahead of the second with its side. V2 skating is done while going down a hill or on a flat area. It involves poling with every stride of the ski.