The wavelength is the peak-to-peak distance of a wave. For sea waves this may vary form a few centimetres for ripple to may metres for deep sea waves. For sounds this varies from a few centimetres for notes at the top of a piano to several metres for those at the bottom. For light the wavelength is between around 400nm (violet) to 700nm (red). This is to be contrasted with the frequency, which os the time taken for the wave to move for. peak-to-peak at a fixed location. For sound waves the two are relatred by the speed of sound, for electriomagnetic waves the speed of lught:
wavelength / frequency = speed
Used in Chap. 14: page 224
Wavelength – peak-to-peak distance