Galaxy clusters are vast groups of galaxies bound together by gravity. They are the largest known structures in the universe, containing hundreds to thousands of galaxies, along with hot gas and dark matter. These clusters can span millions of light-years across and play a crucial role in the formation and evolution of galaxies. Studying galaxy clusters helps astronomers understand the large-scale structure of the universe and the behavior of dark matter. Notable examples include the Virgo Cluster and the Coma Cluster, which provide valuable insights into cosmic history and the dynamics of galaxy formation.