What is the term for a steep drop in a river?

A steep drop in a river is commonly referred to as a waterfall. This term specifically describes the point where water flows over a vertical drop or cliff, creating a dramatic and visually striking feature in the landscape. Waterfalls can vary in height and volume, and they are often formed due to geological processes, such as the erosion of softer rock layers beneath harder rock, leading to steep gradients in the riverbed.

In contrast to waterfalls, rapids are characterized by fast-flowing, turbulent water but do not necessarily involve a significant vertical drop. A watershed refers to the area of land that drains into a particular river or body of water, which is unrelated to the concept of a drop in elevation. A cascade may involve smaller drops of water over a rocky surface, but it does not convey the grandeur or the height associated with what is typically described as a waterfall. Thus, the term 'waterfall' is the most accurate descriptor for a steep drop in a river.