Is a system formed by two stars whose orbital plane is oriented towards the Earth, in such a way, that from our perspective, they undergo mutual eclipses and transits.
Eclipsing binaries are the principal sources of information on the masses and radii of stars. A complete analysis of the light curve can yield the radii of the stars (in units of their separation); orbital characteristics such as eccentricity, orientation in space, and tilt with respect to Earth; and even the surface temperatures of the stars. Kepler’s third law relates the orbital period, the separation of the stars, and the sum of their masses. From observations of the periodic shifts of each star’s spectral lines due to motion of the star toward or away from Earth (the Doppler effect), astronomers can determine the velocity along the line of sight of each star in its orbit. The ratio of the stellar masses then follows from their velocities. With the sum and ratio of the masses in hand, both masses can be determined.
You can learn more about eclipsing binary stars here .