A wing is a type of fin that produces lift while moving through air or water. Drag occurs at the same time and is undesirable as it wastes some of the fuel required to move the wing. Wings are defined by two shape characteristics, an airfoil section and a planform. Wing efficiency is expressed as lift-to-drag ratio. Aerodynamics is the study of wing performance in air.
Wings used in water include various foils, including hydrofoils. Applications of underwater foils include hydroplanes, sailboats and submarines. Hydrodynamics is the study of wing performance in water.