The definition of dwarf planet as stated by the International Astronomical Union (IAU) in 2006 is “a celestial body orbiting a star that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium.”Since 1930, Pluto was considered as part of planet in our solar system. However, in 2006, as scientists had discover several other rocky bodies similar in size or larger than Pluto, the IAU decided to redefined a planet. For an object to be a planet it need to meet these three criteria which are : it needs to be orbiting the Sun, it need to have gravity that enough to pull itself in spherical shape and it needs to have cleared the neighbourhood of its orbit. Pluto doesn’t meet with the third criteria thus, it been classified as dwarf planet since 2006.
In our solar system there are 5 known dwarf planet, Pluto, Ceres, Haumea, Makemake, and Eris. Aside from Ceres who located at the Asteroid Belt, other dwarf planets are located at the Kuiper Belt.