(1) The process by which electromagnetic energy is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space. This concept is to be distinguished from conduction and convection. Also, the process by which energy is propagated through any medium by virtue of the wave motion of that medium, as in the propagation of sound waves through the atmosphere. Also called Radiant Energy and electromagnetic radiation. (2) The outward flow of energy from any Source in the form of radio waves.