The Michelson interferometer is an optical instrument used to measure the interference of light waves. It splits a beam of light into two paths using a beam splitter, reflecting each beam back to recombine them. The resulting interference pattern can reveal information about the light's wavelength and other properties. This device was invented by Albert A. Michelson in the late 19th century and has applications in various fields, including metrology, spectroscopy, and astronomy. It played a crucial role in the famous Michelson-Morley experiment, which tested the existence of the luminiferous ether.