Gravitational lensing is a phenomenon in which the gravitational field of a massive object, such as a galaxy or a cluster of galaxies, bends and distorts the light coming from more distant objects behind it. This distortion can cause the background object to appear magnified, stretched, or even duplicated. Gravitational lensing provides astronomers with a powerful tool to study the distribution of dark matter in the universe, measure the mass of galaxy clusters, and probe the properties of distant galaxies. It has also been used to discover new galaxies and to study the phenomenon of dark energy.