Medium

 A wave medium is the substance which carries a wave (or disturbance) from one location to another. The wave medium is not the wave and it doesn't make the wave; it merely carries or transports the wave from its source to other locations.

Waves propagate through a medium with velocity //c////w// = νλ, where ν is the [|frequency] and λ is the [|wavelength] of the electromagnetic waves. A transmission medium is a material substance (solid, liquid, or gas) which can propagate energy waves. By Jamie Engle

A medium is any material, substance or system through which a wave can propagate. As a wave propagates through a medium, the individual particles that make up the medium transfer energy from one particle to the next and then return to their original state. The medium does not propagate with the wave.
 * Medium **