Planet Definition

RESOLUTION B5 

Definition of a Planet in the Solar System 

(1) A planet is a celestial body that  

    (a) is in orbit around the Sun, 

    (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and  

    (c) has cleared the neighbourhood around its orbit. 

(2) A "dwarf planet" is a celestial body that  

    (a) is in orbit around the Sun, 

    (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, 

    (c) has not cleared the neighbourhood around its orbit, and  

    (d) is not a satellite. 

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies." 

        These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

From the International Astronomical Union

Link to Official IAU Document