What is "supercavitation"

n. (context physics English) An extreme form of cavitation in which a single bubble of gas forms around an object moving through a liquid, significantly reducing drag.

Supercavitation is the use of cavitation effects to create a bubble of gas inside a liquid large enough to encompass an object travelling through the liquid, greatly reducing the skin friction drag on the object and enabling achievement of very high speeds. Current applications are mainly limited to projectiles or very fast torpedoes, and some propellers, but in principle the technique could be extended to include entire vehicles.