There have been varies theories explaining the production of lift by an airfoil. Interestingly, many rather most of these have been misconceived and hence are false. This lists the major theories proposed and the drawbacks they suffer finally leading to a correct acceptable theory.
A fluid flowing past the surface of a body exerts a force on it. Lift is defined to be the component of this force which is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the fluid-dynamic force