Telemark skiing is a downhill skiing technique appropriate for use with free-heel skis, like the ones used in nordic skiing, but usually sturdier. Telemark skiing is named for, and was developed in, the town of Telemark, Norway, when its citizens were competing against the nearby town of Christiana in ski jumping competitions. Christiana developed the Stem Christiana turn, now known as the Stem Christie, which evolved into the alpine technique used in modern downhill skiing. Telemark developed the Telemark turn, in which fore-and-aft stability is achieved by putting one foot in front of the other, bending the knees, and raising the rear heel. By contrast, alpine technique gives fore-and-aft stability by affixing the heel securely to the ski so you can cantilever the ski by pressing on the boot with your shin.

The Telemark technique is especially appropriate to winter travel and ski mountaineering, because it can be used on nordic skis (although the trade-off between speed on the flat and downhill turning control is affected by the heaviness and stiffness of your gear). Telemarking is also practiced at ski resorts. It's harder on the thighs than alpine skiing, but can be much easier on the knees.

If you're interested in the Telemark technique, check out "Free-heel Skiing", by Paul Parker, ISBN 0898864127. I have no affiliation with the author, publisher, etc. This is simply the best book I've found.

See also telemark skiing.