- the geographical line indicating the beginning of a plateau, usually marked by many waterfalls and rapids
- Skiing the line of direct descent down a hill
the line east of the Appalachian Mountains, marking the end of the coastal plains and the beginning of the Piedmont Plateau
- The steepest possible line of descent from a given point on a slope.
- A line connecting the waterfalls of upland rivers before they reach a common coastal plain, often marking the limit of upstream navigation and indicating a zone of potential water power for industrial purposes.