Aeroelasticity is the science which studies the interactions among inertial, elastic, and aerodynamic forces. It was defined by Arthur Roderick Collar in 1947 as "the study of the mutual interaction that takes place within the triangle of the inertial, elastic, and aerodynamic forces acting on structural members exposed to an airstream, and the influence of this study on design." In more simple terms, it is the same set of conditions causing a flag to flutter in a stiff breeze or a reed to tremble in fast-flowing water. Flutter may occur in any fluid medium.
Read more about Aeroelasticity: Introduction, Steady Aeroelasticity, Dynamic Aeroelasticity, Other Fields of Study, Prediction and Cure, Media, Flutter Induced By Dry Friction