IAU definition of planet
The International Astronomical Union (IAU) adopted in August 2006 the definition made by Uruguayan astronomers Julio Ángel Fernández and Gonzalo Tancredi that stated, that in the Solar System, a planet is a celestial body that:is in orbit around the Sun,
has sufficient mass to assume hydrostatic equilibrium, and
has "cleared the neighbourhood" around its orbit.
Source: Wikipedia
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