Circumstellar interaction refers to the process in which a star interacts with the material surrounding it, such as a circumstellar disk or other objects in its immediate vicinity. This interaction can result in the exchange of material, energy, and momentum between the star and its surroundings, leading to various phenomena such as mass loss, accretion, and the formation of planetary systems. Understanding circumstellar interaction is important for studying the evolution of stars, the formation of planetary systems, and the dynamics of stellar environments. Researchers in this field study the physical processes involved in circumstellar interaction and their impact on the properties and behavior of stars and their surrounding environments.