Scientific definition: Radio communication is typically in the form of AM radio or FM Radio transmissions. The broadcast of a single signal, such as a monophonic audio signal, can be done by straightforward amplitude modulation or frequency modulation. More complex transmissions utilize sidebands arising from the sum and difference frequencies which are produced by superposition of some signal upon the carrier wave. For example, in FM stereo transmission, the sum of left and right channels (L+R) is used to frequency modulate the carrier and a separate subcarrier at 38 kHz is also superimposed on the carrier. That subcarrier is then modulated with a (L-R) or difference signal so that the transmitted signal can be separated into left and right channels for stereo playback. In television transmission, three signals must be sent on the carrier: the audio, picture intensity, and picture chrominance. This process makes use of two subcarriers. Other transmissions such as satellite TV and long distance telephone transmission make use of multiple subcarriers for the broadcast of multiple signals simultaneously. http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/bcast.html ^^ I have no idea what they are talking about. Here are the easier to understand Wikipedia pages: http://en.wikipedia.org/wiki/FM http://en.wikipedia.org/wiki/Amplitude_modulation