Plain English Meaning
The study of how an airplane behaves in the air — what makes it climb, descend, turn, accelerate, or stall — based on the four forces acting on it and how the pilot's inputs and conditions change those forces.
Full Definition
The branch of aerodynamics that deals with the forces, motions, and behavior of an aircraft as it moves through the air, including how lift, weight, thrust, and drag interact to produce controlled flight and how those interactions change with airspeed, attitude, configuration, and load factor.