Occultations, Transits and Eclipses
An occultation occurs when an apparently larger body passes in front of an apparently smaller one. A transit occurs when an apparently smaller body passes in front of an apparently larger one. In the combined case where the smaller body regularly transits the larger object, an occultation is also termed a secondary eclipse.
An eclipse occurs when a body disappears or partially disappears from view, either by an occultation, as with a solar eclipse, or by passing into the shadow of another body, as with a lunar eclipse (thus both are listed on NASA's eclipse page).
Transits, occultations and eclipses in general are all effects of a syzygy.
Transits and occultations of the sun by Earth's moon are called solar eclipses regardless of whether the sun is completely or partially covered. By extension, transits of the sun by a satellite of a planet may also be called eclipses, as with the transits of Phobos and Deimos shown here, as may the passage of a satellite into the planet's shadow, as with this eclipse of Phobos. The term eclipse is also used more generally for bodies passing in front of one another. For example, this entry from NASA's Astronomy Picture of the Day refers to the Moon eclipsing and occulting Saturn interchangeably.
Read more about this topic: Occultation