Lensing is a research area in astrophysics that deals with the phenomenon of gravitational lensing, which occurs when light from a distant object is bent or distorted by the gravitational field of a massive object, such as a galaxy or a black hole. This distortion can cause the distant object to appear magnified, stretched, or even multiple times in the sky. Gravitational lensing is an important tool for astronomers to study the distribution of dark matter in the universe, as well as to probe the properties of galaxies and other massive objects.