multiple star

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A system of three or more stars bound together by gravity and orbiting a common center of mass, appearing as a single star when visible to the unaided eye.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun astronomy Multiple stars which form a stellar system, such that they orbit the point of equilibrium of their gravitational fields; a multiple star system.
• noun astronomy Multiple stars that appear to be one when seen with the naked eye, either because they orbit one another (multiple star systems) or happen to be in the same line of sight even though they are separated by a great distance.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a system of three or more stars associated by gravity