A planet is an object orbting a star in space. The Solar System is known to have 8 planets. Pluto is no longer a planet.
After 2006, a planet is something that is in orbit around the Sun, has enough mass so that it has a nearly round shape, and has "cleared the neighbourhood" around its orbit. 'Clearing the neighbourhood' means that the
planet must have enough gravity to pull the asteroids towards the planet or change the path asteroid so that the asteroid do not remain in or around the orbit of planet.