As recognized by the International Astronomical Union, any body which has achieved hydrostatic equilibrium (is reasonably spherical), orbits the sun, and has not "cleared its neighbourhood" (as opposed to a planet)
A dwarf planet is a celestial body within the Solar System that satisfies the following four conditions: 1.) is in orbit around the Sun. 2.] has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (near-spherical) shape. 3.] has not cleared the neighbourhood around its orbit. 4.] is not a satellite