A galaxy cluster is a structure that consists of hundreds of galaxies bound by gravity. Galaxy clusters are much larger than galaxy groups. One of the key features of clusters is the Intracluster medium or ICM. The ICM consists of gas between the galaxies and has a temperature on the order of 7-9 keV. Clusters of galaxies should not be confused with star clusters such as open clusters, which are structures of stars within galaxies, as well as globular clusters, which typically orbit galaxies.