Pluto is classified as a dwarf planet because it meets two of the three criteria set by the International Astronomical Union (IAU) for being a full- sized planet, but fails the third. Specifically, Pluto:

• Orbits the Sun.
• Has enough mass to assume a nearly round shape due to its own gravity.

However, Pluto has not cleared its neighboring region of other objects in its orbit. This means Pluto shares its orbital zone with other objects in the Kuiper Belt and is not gravitationally dominant in its vicinity. Therefore, Pluto is designated a dwarf planet because it does not meet the full definition of a planet, mainly due to its inability to clear its orbital neighborhood.

Key Criteria for Planets by the IAU

• Orbit around the Sun.
• Sufficient mass for a nearly round shape.
• Cleared the neighborhood around its orbit.

Pluto passes the first two but fails the third, leading to its reclassification in 2006.

Additional Context

• Pluto is part of a group of similar icy bodies in the Kuiper Belt beyond Neptune.
• The discovery of other objects similar in size and nature to Pluto in this region led to the need for a clearer definition of planets.
• Pluto's orbit is also eccentric and overlaps with other objects, reinforcing its dwarf planet status.

In summary, Pluto is a dwarf planet because it orbits the Sun and is spherical but has not cleared its orbital path of other debris and objects, distinguishing it from the eight recognized planets in the solar system.