The International Astronomical Union’s General Assembly in August 2006 decided that a celestial body in order to be a planet would need to:
1. be in orbit around Sun
2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
3. has cleared the neighborhood around its orbit.

Pluto was not fulfilled by the third condition and was thus removed by the family of planets (https://www.bbc.com/news/science-environment-33462184). Bodies in the Pluto region were named dwarf planets (https://www.space.com/15216-dwarf-planets-facts-solar-system-sdcmp.html).