The Theodorsen function is a mathematical tool used in aerodynamics to analyze the unsteady aerodynamic forces acting on a wing or airfoil. It describes the relationship between the lift generated by the airfoil and the angle of attack, particularly during oscillations. This function is essential for understanding how aircraft respond to changes in flight conditions. Developed by Theodor Theodorsen in the 1940s, the function is particularly useful in the study of flutter, a phenomenon that can lead to structural failure in aircraft. By providing a way to calculate lift in dynamic situations, the Theodorsen function helps engineers design safer and more efficient aircraft.