Watershed

The geographically defined region within which all water drains through a particular system of rivers, or other water bodies; watershed are defined by “watershed divides” (high points or ridges on the land) and includes hills, slopes, lowlands, floodplains and receiving body of water.

Strictly a water parting, the dividing line between catchment areas. The use of this term as a synonym for catchment or drainage area is deprecated.