A binary star system consists of two stars that orbit around a common center of mass. These stars are gravitationally bound to each other, meaning they influence each other's motion and brightness. Binary systems can be classified into two main types: visual binaries, which can be seen separately through telescopes, and spectroscopic binaries, which are identified by analyzing their light spectra. Binary star systems are important for astronomers because they provide valuable information about stellar masses and evolution. By studying the orbits and characteristics of the stars, scientists can better understand how stars form, evolve, and interact with one another in the universe.