A moon is a natural satellite that orbits around a larger object like a planet. A natural satellite is different from a human made satellite because natural satellites are produced naturally. Moons usually have a stable orbit. This means that the rate of which the moon circles around the planet is just the right speed. If the orbit is too fast or too slow, it is an unstable orbit.
The Moon, which orbits Earth is actually a piece of the planet that was knocked off by a comet or asteroid. In the early stages of the Earth’s formation, a giant comet or asteroid impacted Earth and caused a giant cloud of material and rocks to form. That material came together to become the Moon!