A drainage basin, or watershed, is a geographical area of land where all the surface runoff drains into a common body of water, such as a river, lake, or ocean. These basins are fundamental units of study in hydrology and physical geography, as their boundaries are defined by elevated ridges or divide lines that separate runoff paths. The physical characteristics of a drainage basin—including its slope, underlying geology, and vegetation cover—dictate its hydrological regime, influencing rates of erosion, sediment transport, and the overall chemistry of the water leaving the system. The flow dynamics within a basin are critical components of the global water cycle, as the collected runoff contributes to fluvial processes that shape topography and sustain downstream ecosystems.