Erosion is used in medicine to refer to the eating away of the surface tissue by chemical or physical processes. In geography, erosion is used to describe the gradual wearing away of the earth’s surface by the natural elements of water, ice and frost or wind.
Erosion is a natural process that causes things to break apart and move away from their source. Water, wind and tillage are the main types of erosion. You can find more information here: http://www.wisegeek.com/what-is-erosion.htm