Self-trapping is a phenomenon that occurs when a particle, such as an electron, becomes localized in a specific region of a material due to interactions with its surroundings. This localization can happen in various systems, including semiconductors and insulators, where the particle is unable to move freely because of potential energy barriers created by defects or impurities in the material. In many cases, self-trapping can lead to the formation of localized states, which can affect the electrical and optical properties of the material. Understanding self-trapping is important in fields like condensed matter physics and materials science, as it can influence the behavior of materials used in devices like transistors and solar cells.