The de Broglie wavelength is a concept in quantum mechanics that describes the wave-like behavior of particles. According to Louis de Broglie, every moving particle, such as an electron, has an associated wavelength, which is inversely proportional to its momentum. This means that faster particles have shorter wavelengths, while slower particles have longer wavelengths. The formula for calculating the de Broglie wavelength is λ = h/p, where λ is the wavelength, h is Planck's constant, and p is the momentum of the particle. This idea helps explain phenomena like electron diffraction, where particles exhibit wave-like properties, leading to patterns that can be observed in experiments.