Theodorsen is a mathematical model used in aerodynamics to describe the behavior of oscillating airfoils, particularly in relation to lift and drag forces. Developed by J. Theodorsen in the 1930s, this theory helps engineers understand how wings and other surfaces interact with airflow during various flight conditions. Theodorsen's work is significant in the field of aerospace engineering, as it provides insights into the stability and performance of aircraft. The model is particularly useful for analyzing the effects of unsteady flow, which occurs when an aircraft maneuvers or experiences turbulence, allowing for better design and optimization of flight vehicles.