The wavelength is a property of a wave that is the distance between identical points between two successive waves. The distance between one crest (or trough) of one wave and the next is the wavelength of the wave. In equations, wavelength is indicated using the Greek letter lambda (λ).
The wavelength of light determines its color and the wavelength of sound determines the pitch. The wavelengths of visible light extend from about 700 nm (red) to 400 nm (violet). The wavelength of audible sound range from about 17 mm to 17 m. Wavelengths of audible sound are much longer than those of visible light.
The wavelength λ is related to the phase velocity v and the wave's frequency f by the following equation:
λ = v/f
For example, the phase speed of light in free space is approximately 3×108 m/s, so the wavelength of light is the speed of light divided by its frequency.