The International Astronomical Union (IAU) Prague General Assembly adopted the following definition on August 24, 2006. A "planet" is a celestial body that
(a) is in orbit around the Sun,
(b) has enough mass for its gravity to make the object have a (nearly) round shape, and
(c) has cleared other large objects from the region it crosses during its orbit. (Its gravity caused other orbiting objects to impact, or crash into, its surface or be ejected from our solar system.)
Unfortunately, Pluto does not meet requirement (c).

Smithsonian National Air & Space Museum
Washington, DC

11.28.22