Eclipses occur when a planet casts a shadow on a satellite or vice-versa. The term often refers specifically to eclipses of the Sun and Moon, in which case the planet involved is Earth.
An occultation is when a solar system body blocks the view of a star other than the Sun.
A transit is the apparent passage of a solar system body other than the Moon across the face of the Sun. The only visible transits are those of Mercury and Venus.