Waves of energy which consist of a combination of electric and magnetic fields at right angles to each other: Such electromagnetic radiation results commonly from the acceleration of an electric charge, and is propagated in a vacuum at the speed of light.

The whole range of radiation which extends from high-energy gamma rays to low-energy radio waves: The electromagnetic spectrum is the range of wavelengths, or frequencies, over which electromagnetic radiation is propagated.

The longest wavelengths, or lowest frequencies, are those of radio waves, and the shortest wavelengths are those of gamma rays.