__________ is a highland area which seperates the headstreams of rivers flowing in different directions but rising from the same mountainous source

The term that fits the given definition is "watershed." A watershed is a highland area that separates the headwaters of rivers that flow in different directions but originate from the same mountainous source. Think of it as a dividing line that determines which direction rainwater will flow. Rain that falls on one side of the watershed will flow into one river, while rain that falls on the other side will flow into a different river. This separation is important because it affects the water quality and quantity of each river, and it can have significant impacts on the ecosystems that depend on those rivers.