When a wing is propelled through the air, there is a force upward on the wing due to the Bernoulli effect (air passing more quickly over the top of the wing than the bottom of the wing produces a lower pressure on the upper surface, hence a lift). There is also an upward force due to the air deflected downward from the bottom of the wing. These two forces taken together tend to lift the wing against gravity and is therefore known as LIFT.