A river basin is the area of land where all the water that drains into a specific river and its tributaries collects. This includes rainwater, melting snow, and groundwater that flows into the river system. River basins can vary in size, from small streams to large rivers like the Amazon or Mississippi. The boundaries of a river basin are defined by watersheds, which are elevated areas such as hills or mountains that separate one basin from another. Understanding river basins is important for managing water resources, preventing flooding, and protecting ecosystems within the area.