A waterfall is a water feature along a stream with a vertical drop in the stream bed. This drop causes the water to fall over an edge, giving the term its defining characteristic.
There are many descriptive names used for waterfalls. There are "cataract" waterfalls, which are big, powerful and often associated with rapids, and "cascade" waterfalls, which have several levels or steps as the water descends. If the water simply plunges over an edge and free falls into a pool below, it is called a "plunge" waterfall.
If a wide stream simply falls over an equally wide edge presenting the appearance of a falling sheet of water, it is a "sheet" waterfall. If the water going over stays in contact with the rock face of the falls it can be described as a "horsetail" waterfall. There are also "tiered" waterfalls in which the water goes over one edge and lands in a pool, but it then immediately falls over another edge.
A waterfall can be natural or artificial depending on whether human intervention was involved in making it. A waterfall could be described by the volume of water that goes over it as well as how the volume varies by season or flood stage. A waterfall can also be described by its width, height, the mist produced, its sound and its general appearance. Waterfalls can be tricky to define scientifically, and geologists often do not agree as to where the true beginning and end of a waterfall is located.