Aerodynamic lift is distinguished from other kinds of lift in fluids. Aerodynamic lift requires relative motion of the fluid which distinguishes it from aerostatic lift or buoyancy lift as used by balloons, blimps, and dirigibles. Aerodynamic lift usually refers to situations in which the body is completely immersed in the fluid, and is thus distinguished from planing lift as used by motorboats, surfboards, and water-skis, in which only a lower portion of the body is immersed in the lifting fluid flow.