1. A form of propagated energy, arising from electric charges in motion, that produces a simultaneous wavelike variation of electric and magnetic fields in space. The highest frequencies (or shortest wavelengths) of such radiation are possessed by gamma rays, which originate from processes within atomic nuclei. As one goes to lower frequencies, the electromagnetic spectrum includes x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. 2. Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, Xrays, ultraviolet, visible, and infrared radiation, and radar and radio waves.