Hooookay...the International Astronomical Union (IAU) just released the new definition of "planets" and a new category, "dwarf planets."
(1) A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
As an add-on, Wikipedia defines trans-Neptunian objects as objects in the solar system that orbit the sun at a greater distance on average than Neptune. This has three divisions--the Kuiper belt, Scattered disk, and Oort cloud.
There are now eight classical planets-- everyone except Pluto.
Pluto is now a dwarf planet, and part of a new category of Trans-Neptunian objects accoring to the IAU. New objects will be added to this new category, with Pluto as the prototype.
Charon is also now a dwarf planet. It used to be known as Pluto's moon, but I guess it isn't anymore since dwarf planets exclude satellites.
Ceres, formerly an asteroid, is now a dwarf planet.
Xena, whose name might change, is now a dwarf planet.
Whew! And to think that original proposals went as far as 12 planets, even more. Buti naman at isang planeta lang ang ipinagbago. Mas matipid sa mga teksbuks--tapal action with White-Out.