Drainage basin

"That area, measured in a horizontal plane, enclosed by a topographic (drainage) divide from which direct surface runoff from precipitation or snowpack runoff normally drains by gravity into the stream above the specified point." (United Nations Publications, 2013) 

Sources

United Nations Publications. "Glossary of Shared Water Resources (English-Arabic): Technical, Socioeconomic and Legal Terminology." (2013). DOI:https://dx.doi.org/10.18356/70b462ce-en