A waterfowl (family Anatidae) belonging to one of three genera: Anser (grey goose); Branta (black goose), and Chen (white goose). The greylag goose is Anser anser and the domesticated goose is A. anser domesticus (= A. cygnoides); the Canada goose is Branta canadensis. Many birds that are called geese are more correctly described as swans or ducks. They occur worldwide.