A star cluster is a group of stars that are bound together by gravity. A GALAXY is a large collection of stars, gas, and dust held together by gravity. An ENTOURAGE is a group of people accompanying someone important. A MOB is a large, disorderly crowd of people. Therefore, a star cluster is a group of stars held together by gravity, similar to a GALAXY, but on a much smaller scale. An ENTOURAGE is a group of people accompanying someone important, and a MOB is a large, disorderly crowd of people.