Headcutting is a geomorphological process where a stream or river erodes its channel, causing a sudden drop in elevation. This typically occurs when water flows over a resistant material, leading to the formation of a waterfall or ledge. Over time, the erosive force of the water can cause the headcut to move upstream, resulting in increased erosion and changes to the landscape. Headcutting can significantly impact ecosystems and sediment transport in river systems.