A floodplain is the flat, low-lying area adjacent to a river that is subject to periodic flooding. Floodplains are formed by the deposition of sediments during floods and are characterized by fertile soils and dynamic environments. They are important in hydrology, agriculture, and the study of river dynamics and sedimentary processes.
Reference: Leopold, L. B., Wolman, M. G., & Miller, J. P. (1964). Fluvial Processes in Geomorphology. Dover Publications.