Complex sentence: A carve turn happens when the ski shifts to one side or the other on its edges and lets the ski turn itself be driven by the sidecut geometry while not losing any speed, as happens in a normal parallel turn.
Split into simpler sentences: A carve turn happens when the ski shifts to one side or the other on its edges. In this case, the ski turns itself and is driven by the sidecut geometry while losing no speed, unlike a normal parallel turn.