A knickpoint is a sudden change in the gradient of a river, often seen as a waterfall or a sharp increase in slope. Knickpoints are significant in fluvial geomorphology as indicators of changes in base level, tectonic activity, or variations in lithology. They play a role in river incision and landscape evolution.
Reference: Crosby, B. T., & Whipple, K. X. (2006). “Knickpoint Initiation and Distribution within Fluvial Networks: 236 Waterfalls in the Waipaoa River, North Island, New Zealand.” Geological Society of America Bulletin, 118(7-8), 1051-1066.