In 2006, the International Astronomical Union (IAU) defined a planet as a body in orbit around the Sun that was large enough to have achieved hydrostatic equilibrium and to have " cleared the neighbourhood around its orbit ". The practical meaning of "cleared the neighborhood" is that a planet is comparatively massive enough for its gravitation to control the orbits of all objects in its vicinity. In practice, the term "hydrostatic equilibrium" is interpreted loosely. Mercury is round but not actually in hydrostatic equilibrium, but it is universally regarded as a planet nonetheless.