Wavelength is the physical distance spanned by one complete cycle or wave of an alternating signal as it travels through space. The term wavelength can be applied to many types of wave, e.g. audio, radio, light, etc, but is generally only applicable to a wave of a single frequency, such as the RF carrier transmitted by a mobile phone.
Wavelength (l), usually measured in metres between the adjacent peaks or troughs of consecutive waves, is related to frequency (f) and propagation velocity (v) by the equation l = v / f. Note that the propagation velocity depends on the type of wave and the material through which it passes: radio waves travel at the speed of light, but audio waves at the speed of sound