The various terms related to airfoils are defined below:[6] The suction surface (a.k.a. upper surface) is generally associated with higher velocity and lower static pressure. The pressure surface (a.k.a. lower surface) has a comparatively higher static pressure than the suction surface. The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil. The geometry of the airfoil is described with a variety of terms. A key characteristic of an airfoil is its chord. We thus define the following concepts: The leading edge is the point at the front of the airfoil that has maximum curvature.[7] The trailing edge is defined similarly as the point of maximum curvature at the rear of the airfoil. The chord line is a straight line connecting the leading and trailing edges of the airfoil. The chord length, or simply chord, , is the length of the chord line and is the characteristic dimension of the airfoil section.

A wing is a type of fin with a surface that produces aerodynamic force for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid. As such, wings have an airfoil shape, a streamlined cross-sectional shape producing a useful lift to drag ratio. The word "wing" from the Old Norse vængr[1] 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, or the inverted airfoil on a race car that generates a downward force to increase traction.