Drainage: The term refers to the river system of an area. Small streams join to form a main river that eventually drains into a larger body of water like a lake, sea, or ocean.

Drainage Basin: The area drained by a single river system.

Water Divide: An elevated area, like a mountain or upland, that separates two drainage basins.

The drainage systems in India can be categorised into two major groups based on their region of origin:

The Himalayan Rivers