binary star

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

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

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

• noun astronomy A stellar system that has two stars orbiting around each other; double star.

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

• noun a system of two stars that revolve around each other under their mutual gravitation