Optical depth : A measure of the transparency of a ring system or a cloud. The greater the optical depth, the more light is blocked from passing through the ring. In other words, a ring or cloud with a large optical depth is less transparent than one with a smaller optical depth.

Resonance : A periodic gravitational influence on one orbiting object by another that affects its orbital path.

Shepherd moon : A moon that limits the extent of a planetary ring through gravitational forces.

Trojan moon : A moon that orbits a planet 60 degrees ahead of or behind a large moon.