A natural satellite that orbits a planet or dwarf planet.

Here's why:

* Natural: It's not man-made.

* Satellite: It orbits a larger celestial body.

* Planet or Dwarf Planet: This clarifies that moons orbit planets, not stars.

While we often think of "the Moon" as our own, it's important to remember that many planets in our solar system, and likely beyond, have multiple moons.