Why is Pluto not considered as a planet?

Pluto is not considered a planet because it does not meet all the criteria defined by the International Astronomical Union (IAU) in 2006 for a celestial body to be classified as a planet. Here are the three criteria set by the IAU for a celestial body to be considered a planet:

1. Orbit around the Sun: The body must orbit the Sun.
2. Sufficient Mass for a Nearly Round Shape: The body must have sufficient mass for its gravity to pull it into a nearly round (hydrostatic equilibrium) shape.
3. Clear the Neighborhood around its Orbit: The body must have cleared its orbit of other debris, meaning it must be gravitationally dominant in its vicinity.

While Pluto meets the first two criteria (it orbits the Sun and is nearly round), it fails the third criterion. Pluto shares its orbit with other objects in the Kuiper Belt, a region of the Solar System beyond Neptune filled with icy bodies and debris. It has not cleared its neighborhood of other celestial bodies. Because of this, Pluto was reclassified as a dwarf planet rather than a full-fledged planet. The reclassification demoted Pluto from its status as the ninth planet of the Solar System to one of the many dwarf planets.