The de Broglie wavelength of a particle is a wavelength based on its momentum. The particle's wavelength and momentum are related in the same manner as a photon's. For either:
λ = h/p
Louis de Broglie explored the idea that particles might follow rules analogous to photons, and the consequent predictions are confirmed by experiment, e.g., the behavior of an electron moving toward a slit differs regarding whether another (parallel) slit is nearby, exhibiting the same sort of behavior as does a photon, i.e., showing wave-like interference regarding its apparent flight path. The de Broglie wavelength is a key concept in quantum mechanics, the odd system of mechanics that successfully describes the behavior of such small particles. The waves associated with the particles are termed matter waves or de Broglie waves, and such a wave's frequency is termed its de Broglie frequency.