The wavelength is a unit of relative distance equal to the length of a wave. This could be a light wave, a radio wave, or even a sound wave. For sound waves the formula is:
l=c/f (wavelength = propagation speed/frequency)
In ultrasound imaging is the wavelength the distance between the onset of peak compression or cycle to the next. The wave propagates as bands of compression and rarefaction. One wavelength is the distance between two bands of compression, or rarefaction. Maximum compression corresponds to maximum pressure. The wavelength (see also Angstrom) is important in image resolution.

See also Spectral Reflector.