The removal of part of the land surface by wind, water, gravity, or ice. These agents can only transport matter if the material has first been broken up by weathering. Some writers use a very narrow interpretation of the word, claiming that erosion refers only to the transport of debris; see Stallard in P. Hancock and B. J. Skinner, eds (2000). If so, denudation would be the correct term for the weathering as well as the transport of rocks.
Primary erosion is the initial in situ erosion of rock, regolith, or soil.