Why Pluto is called a dwarf planet?
Pluto is called a dwarf planet because it does not meet all the criteria to be classified as a full-fledged planet. The International Astronomical Union (IAU) redefined the criteria for classifying celestial bodies in 2006, leading to Pluto's reclassification as a dwarf planet.

Criteria for being classified as a planet:
1. Orbits the Sun: Pluto meets this criterion as it orbits the Sun, just like other planets.
2. Round shape: Pluto is spherical in shape, fulfilling this criterion.
3. Cleared its orbit: This is where Pluto falls short. It shares its orbit with other celestial bodies within the Kuiper Belt, a region beyond Neptune. Because it has not cleared its orbit of other debris, it cannot be considered a planet.

Characteristics of a dwarf planet:
1. Small size: Dwarf planets are typically smaller than regular planets, and Pluto is relatively small compared to the other planets in our solar system.
2. Orbits the Sun: Like planets, dwarf planets also orbit the Sun.
3. Not cleared its orbit: The main distinction between a planet and a dwarf planet is that a dwarf planet has not cleared its orbit of other debris.

Conclusion:
Pluto's reclassification as a dwarf planet was a result of the IAU's new criteria for classifying celestial bodies. While it shares some characteristics with planets, it falls short in terms of clearing its orbit of other debris. This distinction led to Pluto being labeled as a dwarf planet rather than a full-fledged planet.