Definitions for "Messier object"
During the late 18th century (1759-1781), the French astronomer Charles Messier made a list of 103 fuzzy objects in space in order not to mistake star clusters, galaxies, and nebulae for comets (for which he was searching). More objects were added later, bringing the total to 110. In it, M1 is the Crab Nebula, M2 is a globular cluster in Aquarius, M3 is a globular cluster in Canes Venatici, etc.
Any of the 110 objects catalogued by French astronomer Charles Messier in the late 18th century. Messier was a comet hunter and catalogued these as objects to "avoid," or objects that could be easily mistaken as a comet. They include many of the best nebulae, star clusters, and galaxies that are visible from mid-northern latitudes.
One of the 110 deep sky objects in the catalogue compiled by Charles Messier. Messier’s are comprised of nebulae, galaxies and star clusters.