The area drained by a single river system, comprising a main river and its tributaries, is called its drainage basin or river basin. The term drainage describes the river system of an area. Small streams flowing from different directions come together to form the main river. It has number of tributaries and distributaries. The river ultimately drains into a large water body such as a lake or a sea or an ocean.
The area drained by the main river, its tributaries and distributaries is termed as the river basin. The river Ganga has the largest river basin in India. The river Indus has a larger river basin but most of it lies outside India.
