Stephano is a retrograde irregular satellite of Uranus. It was discovered by Brett J. Gladman, et al. in 1999, and given the provisional designation S/1999 U 2.
Discovery image of Stephano (encircled)
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
Size comparison of Earth and the Moon
Artist impression of Rhea's proposed rings