- an imaginary line, marked by waterfalls and rapids, where rivers descend abruptly from an upland to a lowland.
- (in the eastern United States) the imaginary line between the Piedmont and the Atlantic coastal plain.
- the path of natural descent from one point on a slope to another.
- the natural downward course between two points on a slope
- the edge of a plateau
- a natural junction, running parallel to the E coast of the US, between the hard rocks of the Appalachians and the softer coastal plain, along which rivers form falls and rapids
