electromagnetic radiationn. Energy having both the form of electromagnetic waves and the form of a stream of photons and traveling at the speed of light in a vacuum. The entire range of frequencies and wavelengths of electromagnetic radiation makes up the electromagnetic spectrum.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.electromagnetic radiation n (General Physics) radiation consisting of self-sustaining oscillating electric and magnetic fields at right angles to each other and to the direction of propagation. It does not require a supporting medium and travels through empty space at the speed of light. See also photon Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014electromagnet?ic radia?tion n. radiation consisting of electromagnetic waves, including radio waves, infrared, visible light, ultraviolet, x-rays, and gamma rays. [1950?55] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.electromagnetic radiation Energy that moves through space and matter both in the form of magnetic and electric waves and in the form of a stream of particles called photons.Did You Know? Many people have heard that light is made up of waves, but what does that mean? The answer seems very abstract: light, and other forms of electromagnetic radiation, are made up of wave-shaped electric and magnetic fields that reinforce each other as they travel together. In the 19th century, physicists discovered that a changing electric field can create a magnetic field, and a changing magnetic field can create an electric field. So a wave-shaped electric field (for example, the field created when a charged particle such as an electron moves up and down) can create a wave-shaped magnetic field, which in turn reproduces the wave-shaped electric field. These mutually re-creating fields travel at the speed of light. Electromagnetic radiation can have a variety of properties, depending on its wavelength. Certain wavelengths make up the spectrum of visible light. Infrared light and radio waves have longer wavelengths, whereas ultraviolet light, x-rays, and gamma rays have shorter wavelengths. These wave properties do not tell the full story of electromagnetic radiation, however. Visible light and other forms of electromagnetic radiation also exist as streams of the particles known as photons. The energy of the photons increases as the frequency of the waves gets higher.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.electromagnetic radiationRadiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible, and infrared radiation, and radar and radio waves.Dictionary of Military and Associated Terms. US Department of Defense 2005.electromagnetic radiationWaves of energy associated with electric and magnetic fields.Dictionary of Unfamiliar Words by Diagram Group Copyright © 2008 by Diagram Visual Information Limited