Dwarf planet

Dwarf planets were celestial bodies similar to actual planets, which were nevertheless not considered to fall under the definition of a planet.

Dwarf planets in the Sol system included Eris, Ceres and Pluto.

Although Pluto was not considered to be a planet anymore by Steven Taylor's times (AUDIO: The Anachronauts), some still called it a planet at a much later point in time. (TV: The Sun Makers)