The Compton wavelength shift refers to the change in wavelength of a photon when it scatters off a charged particle, such as an electron. This phenomenon occurs due to the conservation of energy and momentum during the collision, resulting in a longer wavelength for the scattered photon compared to its initial wavelength. This effect is significant in quantum mechanics and demonstrates the particle-like behavior of light. The Compton effect was first observed by Arthur H. Compton in 1923, providing evidence for the dual nature of light and contributing to the development of modern physics.