A basin is a container that holds water and is used for washing, but you probably just call it your bathroom sink.
You can think of basinas something shaped like a bowl. If you're going for an old-fashioned ring, say "wash basin." If you’re in England, you might use a basin for cooking. The word basin also has various geological senses, particularly a depression in the ground or ocean floor. A basin is also the spot where a river drains — like the famed Mississippi River Basin. That’s one big bowl!