1. A combination of processes in which the materials of the earth's surface are loosened, dissolved, or worn away and transported from one place to another by natural agents; such as, wind and rainfall.
2. The group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the earth's surface.
3. The gradual destruction or reduction and weakening of something: "An erosion is an eating away of a surface; for example, a skin erosion is a loss of part or all of the epidermis (the outer layer) leaving a denuded surface or a tooth erosion is a gradual loss of the normally hard surface of the tooth because of chemical reactions or of abrasion or rubbing."

The surface erosion of a material caused by the formation and scallops of cavities when the material is immersed in a liquid environment; for example, the erosion of an operating bronze ship propeller.

Theory was developed or formulated by the American geographer and geomorphologist, William Morris Davis (between 1884 and 1934) who modeled the formation of river-eroded landscapes.

This theory suggests that landscapes go through three stages of development (youth, maturity, and old age) and indicates that the rejuvenation of landscapes arises from tectonic uplift of the land.

In the "youthful stage", under the influence of tectonic uplifts, there appears a mountain relief, which is dissected through erosion (the washing out of rocks by rivers) into deep, narrow valleys and sharp-peaked ridges.

With the dissection by streams, the area would reach maturity and, ultimately, would be reduced to an old-age surface called a peneplain (gently undulating, almost featureless plain), with an elevation near sea level.

The model developed by Davis, though important in historical context, is currently considered only a first approximation.

Developments in the sciences of geology and geomorphology, especially the plate tectonics revolution of the 1960s and 1970s, have confirmed the preliminary nature of the model.

Erosion which is caused by prevailing agencies of the natural environment; including, running water, rain, wind, waves, and organic weathering.

Such erosion is primarily responsible for the present modifications of the land surfaces.

In geology, the detachment and transportation of topsoil by the action of wind and running water: At the seashore, Jeny noticed how much of the coastal line was influenced by soil erosion because, over time, the shoreline had been eaten away by the waves of the sea.