planet
A large spherical astronomical object that typically orbits a star. The tag should be used when at least one planet is seen from outer space or from the surface of another nearby planet. This includes real and fictional planets.
Scientifically, there has always been some ambiguity as to what constitutes a planet, with some celestial bodies such as Pluto and Ceres being considered at different times or by different people either as planets or as "dwarf planets". The International Astronomical Union (IAU) came up with a definition for a planet in 2006, meaning that the planets in our solar system are officially Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and neptune, but the definition remains contentious.