(1) A sinusoidal undulation or vibration, a form of movement by which all radiant Energy of the Electromagnetic Spectrum is thought to travel. (2) A disturbance which is propagated in a medium in such a manner that at any point in the medium the quantity serving as the measure of the disturbance is a function of time, while at any instant the displacement at a point is a function of the position of the point. Any physical quantity having the SAME relationship to some independent variable (usually time) that a propagated disturbance has, at a particular instant, with respect to space, may be called a wave. An Electromagnetic Wave is one in which the disturbance is the change in the electric and magnetic field intensities from their equilibrium values in space.