Kinetic theory is a branch of theoretical physics that describes the behavior of gases, liquids, and solids in terms of the motions and interactions of individual particles. The theory is based on the assumption that these particles are in constant motion and collide with each other and with the walls of their container. By studying these motions and interactions, kinetic theory can explain macroscopic properties of materials such as temperature, pressure, and viscosity. It has applications in a wide range of fields, including chemistry, engineering, and meteorology.