In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly, the landing and take-off speeds will be higher. The high wing loading also decreases maneuverability. The same constraints apply to winged biological organisms.

Wing loadings are usually given in either lb/ft² or kg/m², and occasionally in N/m². Wing loadings of 10 lb/ft², 48.8 kg/m² and 479 N/m² are the same.

The table, which shows wing loadings, is intended to give an idea of the range of wing loadings used by aircraft. Maximum weights have been used. There will be variations amongst variants of any particular type. The dates are approximate, indicating period of introduction.

The critical limit for bird flight is about 5 lb/ft² (25 kg/m²). An analysis of bird flight which looked at 138 species ranging in mass from 10 g to 10 kg, from small passerines to swans and cranes found wing loadings from about 1 to 20 kg/m². The wing loadings of some of the lightest aircraft fall comfortably within this range. One typical hang-glider (see table) has a maximum wing loading of 6.3 kg/m², and an ultralight rigid glider 8.3 kg/m².

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.