Watershed /(?)/

Wa·ter·shed

Watershed

n.
  1. The whole region or extent of country which contributes to the supply of a river or lake.
  2. The line of division between two adjacent rivers or lakes with respect to the flow of water by natural channels into them; the natural boundary of a basin; -- called also divide and water parting.
  3. a point in time marking an important transition between two situations, or phases of an activity; a turning point.