Moon

From Egs Mayhem

A ball o' rock that orbits a planet instead of a star. They're significantly smaller than the planets they orbit (they have to be, otherwise they'd be in binary planet systems instead of being moons), but still big enough to coagulate into a ball o' rock (or a solid clump o' rock) rather than a whole lot of smaller rocks zipping around in orbit.

The Earth's moon may or may not be made of cheese.