what does off-piste mean in skiing and snowboarding

It means ''off the trail.'' Off piste is going off the designated groomed trails on the mountain. Its just wild untamed mountain. You are not supposed to ski or board there because it is not checked for safety and not groomed. a lot of skiers/boarders like to for the thrill and danger and also because it is usually pure, that is no one has skiied on it so the snow is flat. Its also more challenging.

Quite literal go off the piste. A lot of skiers and snowboarders like it because the snow at the side off the piste is looser, it is powder. This powder is mostly also deeper and very loose, this a very different feeling to ride. Further going off piste allows you to go where no people rode before. It gives a kick to a lot of people. Although most important off piste can be very difficult. Because there is nothing done on it so there is a risk at avalanches.