The term "Messier" primarily refers to the Messier Catalog, a list of astronomical objects compiled by the French astronomer Charles Messier in the 18th century. This catalog includes 110 objects, such as star clusters, nebulae, and galaxies, which are often used by amateur and professional astronomers for observation. The catalog helps distinguish these objects from comets, which Messier was primarily searching for. In addition to the catalog, "Messier" can also refer to various astronomical phenomena or objects that are part of this list, such as Messier 31 (the Andromeda Galaxy) and Messier 87 (a giant elliptical galaxy). These objects are significant in the study of the universe and are popular targets for telescopes.