A folding wing is a design feature of aircraft to save space in the airfield, and time, and is typical of naval aircraft that operate from the limited deck space of aircraft carriers. The folding allows the aircraft to occupy less space in a confined hangar because the folded wing normally rises over the fuselage decreasing the floor area of the aircraft. Vertical clearance is also limited in aircraft carrier hangar decks. In order to accommodate for this, some aircraft such as the Supermarine Seafire and Fairey Gannet have additional hinges to fold the wingtips downward, while others such as the S-3 Viking have folding tails.

Short Brothers, the world's first aircraft manufacturer, developed and patented folding wing mechanisms for ship-borne aircraft (Short Folder), the first patent being granted in 1913. The wings were hinged so that they folded back horizontally alongside the fuselage, usually being held in place by latches projecting sideways from the rear of the fuselage.

Since the monoplane supplanted the biplane in the late 1930s, virtually all fixed-wing aircraft designed for shipboard duty have been equipped with folding wings. Notable exceptions include the SBD Dauntless, F2A Buffalo, and A4D/A-4 Skyhawk (all USN types) and the Sea Harrier (British). All four are relatively small designs.

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid. A wing is an airfoil, which has a streamlined cross-sectional shape producing a useful lift to drag ratio.

The word "wing" from the Old Norse vængr for many centuries referred mainly to the foremost limbs of birds (in addition to the architectural aisle.) But in recent centuries the word's meaning has extended to include lift producing appendages of insects, bats, pterosaurs, boomerangs, some sail boats and aircraft.

"Wing" can also mean an inverted airfoil on a race car that generates a downward force to increase traction.

Various species of penguins and other flighted or flightless water birds such as auks, cormorants, guillemots, shearwaters, eider and scoter ducks and diving petrels are avid swimmers, and use their wings to propel through water.

A wing's aerodynamic quality is expressed as its lift-to-drag ratio. The lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.