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How is a dwarf planet different from a planet?

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Pluto Pluto as observed by the New Horizons spacecraft, July 13, 2015.

In 2006, the International Astronomical Union (IAU) established formal criteria to distinguish between a planet and a dwarf planet.

To be classified as a planet, a celestial body must meet three specific conditions:
* It must orbit the Sun.
* It must have sufficient mass for its own gravity to pull it into a spherical or nearly spherical shape.
* It must have "cleared the neighbourhood" around its orbit, meaning its gravity is strong enough to have removed other rocky and icy debris from its orbital path.12

A dwarf planet meets the first two criteria but fails the third; it is not massive enough to have cleared its orbital neighborhood of other objects. Additionally, a dwarf planet cannot be a moon of another body.32

Pluto was reclassified as a dwarf planet because it orbits within the Kuiper belt, sharing its orbital path with other icy debris, rather than dominating its region of space.12