Gamma rays are a form of electromagnetic waves that have the highest frequencies and shortest wavelengths in the electromagnetic spectrum. Electromagnetic waves include various types of waves such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Gamma rays are the most energetic and have the highest frequency and shortest wavelength among all these waves. They are produced by nuclear reactions and radioactive decay, and are commonly used in medical imaging and radiation therapy.