fall line

noun

1. an imaginary line, marked by waterfalls and rapids, where rivers descend abruptly from an upland to a lowland.
2. (initial capital letters) Eastern U.S. the imaginary line between the Piedmont and the Atlantic coastal plain.
3. Skiing. the path of natural descent from one point on a slope to another.

noun

1. skiing the natural downward course between two points on a slope
2. the edge of a plateau

noun

1. 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

1. A line connecting the waterfalls of nearly parallel rivers that marks a drop in land level.