What is the definition of River Source?

In hydrology, the source of a river is the location where the river begins to flow continuously on the surface of the land. This can be a spring, where groundwater discharges onto the surface, a lake or pond, or the confluence of two or more streams. The source of a river is often marked by a distinctive topographic feature, such as a mountain or hill, or by a change in the vegetation. The headwaters of a river are the uppermost streams that feed the main river, and the watershed or drainage basin of a river is the area of land that drains into it.