Cosmic Microwave Background (CMB) lensing is a branch of astrophysical research focused on studying the bending of light from the CMB by large-scale structures in the universe, such as galaxy clusters or dark matter halos. This gravitational lensing effect causes slight distortions in the CMB radiation, providing valuable information about the distribution of dark matter and the large-scale structure of the universe. By analyzing these distortions, researchers can learn more about the formation and evolution of cosmic structures and test theories of cosmology.