Gravitational lensing is a phenomenon predicted by Einstein's theory of general relativity in which the gravitational field of a massive object, such as a galaxy or a black hole, bends the light from more distant objects behind it. This bending of light creates distortions and magnifications in the appearance of the background object, acting as a natural lens in space. Gravitational lensing is used by astronomers to study the distribution of dark matter, measure the masses of galaxies and galaxy clusters, and probe the properties of distant objects that would otherwise be too faint to observe directly.