A moon is a natural satellite of a planet. For Earth's moon, see Luna.
Moons are permanent natural satellites. Following Jupiter's satellite Io, Luna, the Earth's moon, is second-densest satellite among those whose densities are known.
Terraforming[]
Terraforming moons would need the following requirements: an atmosphere dense enough to stay on such a small satellite, more mass, and an abundance of water. A possible solution for the atmosphere could be the dense SF6 gas but it could be harmful if inhaled. Oxygen would have to be mixed with the gas and futher technology would have to be developed to trap the oxygen so it can't escape.