The area of land that is drained by a river is the drainage basin
The answer is drainage basin.
A drainage basin is an area of land drained by a river and its tributaries. The drainage basin comprises water present in the water table and surface run-off. A crest is a ridge of high land (watershed) the divides two separate drainage basins. Rainfall which falls on the other side of the watershed will flow into a river in the adjacent river basin.
