Binary stars are two stars orbiting around a common center of mass, and they are often referred to as double stars. The term "binary star" is commonly used in astronomy to describe this phenomenon, but there are several other terms and synonyms to describe it as well. One such term is "twin stars," which implies that the two stars in question are very similar in size and brightness. Another synonym is "binary system," which acknowledges the fact that these stars are closely related and interact with each other in ways that are not seen in single stars. Regardless of what they're called, binary stars remain an important object of study for astronomers, who continue to gain new insights into this fascinating celestial phenomenon.