A wave is an oscillation in space, with peaks and troughs. The distance from one peak to the next is the wavelength. It is measured in units of distance. The wavelength of ocean water waves will be meters. The wavelengths of visible light corresponds to hundreds of nanometers (billionths of a meter). Wavelength is an important way to characterize a wave. For light, the shorter the wavelength, the higher the energy of the light wave.