A watershed is all of the land around a river or other body of water which drains into it. Watersheds are also called drainage basins or catchments, and are basin-like landforms which capture and release precipitation into a common body of water. They include both urban and rural areas - forests, farms, roads, homes, factories, and communities large and small.
Watersheds connect the land to the water and, because everyone on the planet lives in a watershed, everyone has an impact, good or bad, on water quality.
See the short video "What is a watershed?" by clicking here.