A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
Size comparison of Earth and the Moon
Artist impression of Rhea's proposed rings
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms object and body are often used interchangeably. However, an astronomical body or celestial body is a single, tightly bound, contiguous entity, while an astronomical or celestial object is a complex, less cohesively bound structure, which may consist of multiple bodies or even other objects with substructures.
Composite image showing the round dwarf planet Ceres; the slightly smaller, mostly round Vesta; and the much smaller, much lumpier Eros
Image: 243 ida
Image: Mimas Cassini
Image: Portrait of Jupiter from Cassini