1. Eclipsing binaries are only eclipsing relative to an observer on Earth.

    To be an eclipsing binary, the binary is seen nearly edge-on (i.e., at an inclination relative to the line of sight of nearly 90°).

  2. Eclipsing binaries are usually also spectroscopic binaries which means the time-varying Doppler shift of their spectral lines proves a system is a binary.

    If only one component star's spectral lines are seen the binary is a single-lined spectroscopic binary.

    If spectral lines are seen from both component stars, the binary is a double-lined spectroscopic binary.

  3. Most (maybe all) eclipsing binaries are NOT visual binaries.

    Visual binaries are those that can be resolved into two stars.

    There may be some eclipsing binaries that are visual binaries, but yours truly knows of none.

  4. Eclipsing binaries are very useful because their eclipsing behavior gives extra information:

    1. The determination of stellar masses for spectroscopic binaries cannot be done without knowing inclination.

      All one can determine for a double-lined spectroscopic binary is the quantity m*sin(i)**3, where m is the stellar mass of a component star, i is inclination, and sin is the sine function. We know even less about the stellar mass of single-lined spectroscopic binaries (e.g., Shane Larson: Binary Stars).

      However, for an eclipsing binary, we know inclination i ≅ 90°. So at least for double-lined spectroscopic binaries we can determine the component stellar masses to some accuracy.

      One can, of course, determine mass for stars by modeling and stellar spectroscopic data, but those results are then model-dependent, of course.

    2. Information about the relative stellar radii can be determined directly from the size of the eclipse dips in the light curve (see the lower panel of the animation).

  5. Exoplanets that exhibit transits are somewhat similar to eclipsing binaries.

    1. However, usually the planet cannot be resolved or detected in any way other than through the dips in the light curve.

    2. The planet does a mini-eclipse of the host star when it transits the host star.

    3. There is an even smaller dip when the host star transits the planet since reflected light from the planet is cut off plus an planet from its own internal heat energy.

    4. The two kinds dips are tiny, but can be observed with modern methods.

    5. From the transit measurements, orbital radius and the orbital period of and the planet can be determined.

    6. Sometimes light from the host star passing though the limb of the atmosphere can analyzed with absorption spectroscopy to learn something about the atmosphere composition (see Wikipedia: Exoplanet: Atmosphere).

    7. Detection of exoplanets by transit method is one of the two main methods of detecting exoplanets.

      The other method is the Doppler spectroscopy method.