A drainage basin or catchment basin is an extent or an area of land where all surface water from rain, melting snow, or ice converges to a single point at a lower elevation where the waters join another body of water, such as a river, lake, reservoir, estuary, wetland, sea, or ocean.

Thus if a tributary stream joins a brook that in turn joins a small river which is a tributary of a larger river, there is a series of successively larger (and lower elevation) drainage basins.

Other terms used to describe drainage basins are catchment, catchment area, drainage area, river basin and water basin.

The five largest river basins (by area), from largest to smallest, are the basins of the Amazon, the Río de la Plata, the Congo, the Nile, and the Mississippi.

The three rivers that drain the most water, from most to least, are the Amazon, Ganga, and Congo rivers.

What is a watershed?

A watershed is known by many other names including drainage divide, water divide, divide, ridgeline, water parting etc.

A watershed is an area or ridge of land that separates waters flowing to different rivers, basins, or seas.

A valley floor divide is a low drainage divide that runs across a valley, sometimes created by deposition or stream capture.

What is an Esker?

An esker is a long, winding ridge of stratified sand and gravel. Eskers are frequently several kilometres long.