Gamma rays are a form of electromagnetic radiation, similar to visible light but with much higher energy. They are produced by radioactive atoms and certain types of cosmic events, such as supernovae. Gamma rays have the shortest wavelength in the electromagnetic spectrum, making them highly penetrating and capable of passing through most materials, including human tissue. Due to their high energy, gamma rays are used in various applications, including medical treatments like cancer radiotherapy and in imaging techniques such as PET scans. They are also studied in astrophysics to understand phenomena like black holes and neutron stars.