A planet is a body large enough that, when it formed, it condensed under its own gravity to be shaped like a sphere. It orbits a star directly and is not a moon of another planet.There are at least ten planets. Pluto is a spheroid (as is the Earth), orbits a star directly, and isn't the moon of another planet. Charon, by contrast, orbits Pluto, as do at least two other moons, so Charon and the other two moons are not planets.
Well, the Pluto-Charon system has its barycenter outside of both bodies, so it could be argued that the Pluto-Charon system is a double-planet, while Nix and Hydra orbit the two.