A dwarf planet, in the International Astronomical Union's 2006 Solar-system definition, is a body that orbits the Sun, has enough self-gravity to assume a nearly round hydrostatic equilibrium shape, has not cleared its orbital neighborhood, and is not a natural satellite. The classification combines a body's physical shape with its dynamical environment; it is not defined by size alone.[ref]
Definition of a Planet in the Solar System by the International Astronomical Union. Adopted planet-definition resolution, category 2 and its four criteria
Pluto illustrates why both aspects matter: it is rounded but belongs to the trans-Neptunian population rather than being dynamically dominant in its orbital region. Ceres provides another example, in the asteroid belt. A rounded Moon does not become a dwarf planet, because the satellite exclusion is explicit. Under this terminology, planet and dwarf planet are distinct categories.[ref]
Definition of a Planet in the Solar System by the International Astronomical Union. Adopted categories and accompanying classification of Pluto and Ceres
Clearing does not mean that literally no other object shares the region. It concerns orbital dominance over the surrounding population. Nor does the rounding requirement supply one universal diameter threshold: resistance to deformation depends on composition, internal structure and rotation. Observations of shape and mass therefore address one part of the definition, while orbital-population information addresses another. The cited resolution is explicitly about the Solar system; applying the same wording to an exoplanet population requires an additional convention.
