Regolith is the loose solid material (i.e., not liquid or atmosphere) on a body, i.e., other than the body's solid rock. Examples of regolith include dirt, sand, small rocks, ash, and biological material. The term is applied to Earth, the Moon, and other planets, moons, and asteroids/etc., and is used when characterizing the surface of such a body. The amount and character of regolith can be of interest in determining how to land a vehicle on a body and what and how surface material can be analyzed or retrieved. For example, before the first Moon landings, it was considered whether its surface might be dust of a sort which would not support a lander. Regolith can include ice, e.g., on Earth, Mars and some outer moons.
The phrase regolith scale has been used to characterize the depth of a study of a planet or moon's surface. It implies "on the order of a few meters depth".