Instruction: What is a planet ?

Response: The International Astronomical Union (IAU) defined in August 2006, that a planet in the Solar system is a celestial body that :
- orbits the Sun (the host star of the Solar system), 
- has enough mass to assume a hydrostatic equilibrium (nearly round) shape,
- is big enough that its gravity cleared away any other similarly-sized objects near its orbit around the Sun.