Size no longer matters

The IAU has spoken.

The scientists decided to be scientists, and not politicians.

Classical Planet:

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 cleared the neighborhood around its orbit.

Dwarf planet: (currently Pluto, Ceres, and ‘Xena’, with a dozen more potential Dwarfs being analyzed)

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 neighborhood around its orbit
(d) is not a satellite.

Small Solar System Bodies:

Anything else.