The correct answer to this open question is the following.
The geographical dividing line between the tidewater and Piedmont in Virginia was known as the Fall Line.
The meaning of Piedmont in Virginia was "the foot of the mountain." It was the land that was at the foot of the mountains. Let's remember that Virginia was dived into three regions: Mountains, Piedmont, and Coastal Plain. The eastern boundary of Piedmont is the Fall Line. Here, the land is sharp and some waterfalls make navigation difficult.