- A planet is a celestial body that is massive enough to be rounded by its own gravity and is usually orbiting a star.
- A planet proper has a mass greater than Pluto's mass and less massive than ten times Jupiter's mass 
- A planet proper is part of the Solar System.
- Has cleared the neighborhood around its orbit.
- A planet that has not cleared the neighborhood around its orbit is called a dwarf planet.
- A celestial body that meets a planet requirement but is located outside the Solar System is called an exoplanet.
- Smaller planets that are not massive enough to be rounded by their own gravity are called minor planets.