An airfoil is any part of an aircraft that is designed to produce lift. The wing is the primary airfoil but the propeller can also be an airfoil as well as the tail surfaces or sometimes even the fuselage itself. An airfoil has a leading edge, a trailing edge, a chord, and camber. The leading edge is the "front" of the airfoil—the portion that meets the air first. The trailing edge is the back of the airfoil—the place at which the airflow over the upper surface of the airfoil joins the airflow over the lower surface of the airfoil.
The chord of an airfoil is the imaginary straight line drawn through the airfoil from its leading edge to its trailing edge. The camber of an airfoil is the curve of its upper and lower surfaces. This curve is measured by how much it departs from the chord of the airfoil. Some airfoils have very little camber, i.e., the airfoil looks flat, while others have a higher degree of camber—the airfoil has more curve. The term upper camber refers to the camber of the upper surface of the airfoil. The term lower camber refers to the camber of the lower surface of the airfoil. The camber of an airfoil affects its lift. The direction of the air that is flowing past an airfoil relative to the path of flight is called the relative wind. The relative wind is always parallel and opposite in direction to the path of flight.