Dwarf Planet

A term adopted by the International Astronomical Union (IAU) in 2006 in order to define a celestial body orbiting the Sun that is large enough to be "round" and that shares its orbit with other celestial bodies of comparable size.

As a result of this definition, Pluto is not considered a planet anymore by the IAU, thus reducing the count of known planets in our solar system to eight.

Astronomy

Currently, only two objects in our solar system are proven to be dwarf planets: Ceres in the asteroid belt and Pluto in the Kuiper Belt. The IAU recognizes other three dwarf planets in the Kuiper Belt, though they are not proven to be "round" yet: Eris, Makemake and Haumea. Vesta, Pallas and Hygiea are the only three candidates in the asteroid belt to be dwarf planets, while other candidates orbit in the Kuiper Belt or (supposedly) beyond.

Astrology

This is an astronomical definition that has no impact on astrology: in fact planets in astrology include the Sun, the Moon and, for some astrologers, Ceres, Pallas, Juno, Vesta and Chiron, none of these ever being a planet in astronomy. Thus Pluto is still considered a planet in astrology.