Dwarf planet

A dwarf planet or planetoid is an object which orbits a star, but is spherical and has other objects in its neighborhood. Some people say they could be Planets, but others don't.

History
In 1930, the dwarf planet Pluto got discovered, but it was classified as a planet. This was first questioned in the 90s when people found many Pluto-like objects that are now called plutoids. In 2005, Eris was discovered and was heavier than pluto, so it would either be called the tenth planet, or get demoted to the new classification. The IAU chose the latter,