In astronomy, a syzygy is a straight-line configuration of three celestial bodies in a gravitational system. Transits, occultations and eclipses in general are all effects of a syzygy.
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, or by passing into the shadow of another body.