A (major) Planet is a body of considerable mass that doesn't produce light on its own and orbits a star. Until recently, only nine were known (all of them in the Solar system). As of the middle of 2001 over 60 are known, with all of the new discoveries being extrasolar planets.
Astronomers call asteroids minor planets, and they call what are commonly know as planets, major planets.
The planets of our solar system (in increasing distance from the Sun) are
- Earth -- with its Moon, sometimes considered a "double planet."
- Pluto -- with its moon Charon sometimes considered a double planet, and also sometimes not considered a planet at all, but simply one of the largest of the Trans-Neptunian objects in the Kuiper Belt.