An exciton is a bound state of an electron and a hole, which is created when an electron in a material absorbs energy and moves to a higher energy level, leaving behind a vacancy or "hole." This pair can move through the material together, behaving like a single particle. Excitons are important in the study of semiconductors and insulators, as they play a crucial role in processes like light absorption and energy transfer. Excitons can be found in various materials, including semiconductors, insulators, and even some organic compounds. They are essential for understanding phenomena such as photovoltaic effects in solar cells and the operation of light-emitting diodes (LEDs). Their unique properties make excitons a key focus in the development of new electronic and optoelectronic devices.