A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas and dust, and dark matter. The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Galaxies range in size from dwarfs with just a few thousand (103) stars to giants with one hundred trillion (1014) stars, each orbiting their galaxy's own center of mass.