Galaxy clusters are large groups of galaxies that are gravitationally bound together. They contain hundreds or even thousands of individual galaxies, along with vast amounts of dark matter and gas. Galaxy clusters can range in size from small groups containing just a few galaxies to massive structures like the Virgo Cluster which contains over 1000 galaxies. These clusters are not only important for their sheer number of galaxies but also because they provide valuable information about the large-scale structure of the universe and the distribution of matter within it.