Wavelength and wavenumber are both measures of the properties of a wave, but they represent different aspects of the wave.

• Wavelength (λ) refers to the distance between two consecutive peaks of a wave. It is typically measured in units of length, such as meters. Wavelength determines the color of light, the pitch of sound, and other characteristics of the wave.
• Wavenumber (ν) is the number of wave cycles that pass a fixed point per unit length. It is usually measured in reciprocal units of distance, such as per meter (m^-1). Wavenumber is often used in spectroscopy to describe the energy of a photon, which is proportional to the frequency of the electromagnetic wave.