Pluto has been demoted to a “dwarf planet”.

“a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit.” has become the new definition for a planet.

In short, becuase of its smaller size and elipitcal orbit around the Sun they are creating a new sub-planet category for it.

Personally, I feel slightly upset by this. I suppose its useless to get emotional about an astronomical definition. Still its a little sad.

There apparently was no previous definition for a planet.