The Pleiades (Messier 45), or Seven Sisters, are a star cluster in the constellation of Taurus. It is the most prominent and easiest star cluster to find being easily visible to the unaided eye, indeed most people can see at least seven stars without binoculars or telescopes.

Image: Pleiades star cluster with names of the main stars Atlas, Pleione, Alcyone, Merope, Sterope I, Sterope II, Maya, Taygete, Calaeno and Electra [1]

[1] Star and Planet Spotting: A Field Guide to the Night SkyISBN 0 7137 0655 4