Lift is the lifting force on a flying object (in particular, a wing or a whole aircraft), due to its motion relative to the surrounding air. It must be equal to or greater than the weight of the object in flight and acting in the opposite direction. Lift can be increased by increasing the forward speed of the aircraft or by increasing the angle of attack. Lift is one of the four forces of flight acting on an airplane, the others being weight, thrust, and drag.
The lift-to-drag ratio is the ratio of the lifting force to the drag force for either an isolated wing or a complete aircraft. This ratio is also used in determining the rate of descent of a space vehicle in the atmosphere.