Open star clusters (or "open clusters") are collections of stars—perhaps a few dozen to a few thousand—that likely formed in the same molecular cloud, but are not gravitationally bound to each other. They eventually wander away from each other and find their own paths through the galaxy. Our own sun was probably once part of an open cluster at one time but has since moved out on its own.

Our Milky Way Galaxy is repleat with open clusters, some of which, like the Pleiades and Hyades, are visible to the naked eye and may yet still be surrounded by remnants of the gas and dust clouds that contributed to their formation.