Drainage basin - the area of land drained by a river. Catchment area - the area within the drainage basin. Watershed - the edge of highland surrounding a drainage basin which marks the boundary between two drainage basins. Source - the beginning or start of a river. Confluence - the point at which two rivers or streams join. Tributary - a stream or smaller river which joins a larger stream or river. Mouth - the point where the river comes to the end, usually when entering a sea.
