Erosion or soil erosion is broadly defined as the removal of (top-) soil from the land surface by running water, wind, ice or gravity. It can be accelerated by human activities (tillage) and animals. 

Source: “Status of the World's Soil Resources. Main Report |Policy Support and Governance| Food and Agriculture Organization of the United Nations .” Food and Agriculture Organization of the United Nations (FAO) and Intergovernmental Technical Panel on Soils (ITPS), 2015.