What is meant by a water divide? Give an example.

A vertical landmass or an upland separates two drainage basins in an elevated area. that mountain is known as a water divide. 

For example, Satpura mountain act as the water divide between the Narmada and the Tapi river systems.

A vertical landmass which separates two drainage basins in an elevated area, such upland is known as a water divide. The water dividing of Indus and the Gange river bodies is Ambala which is a good example of it.