Complex sentence: A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary'173 planetary satellites orbiting six of the eight planets, and seven orbiting three of the five IAU-listed dwarf planets.
Split into simpler sentences: A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its "primary". Formally classified moons include 173 planetary satellites orbiting six of the eight planets, and seven orbiting three of the five IAU-listed dwarf planets.