Duck is the common name for a number of species in the Anatidae family of birds. The ducks are divided between several subfamilies listed in full in the Anatidae article. Ducks are mostly aquatic birds, mostly smaller than their relatives the swans and geese, and may be found in both fresh water and sea water.

Goose (plural geese, male gander(s)) is the general English name for a considerable number of birds, belonging to the family Anatidae. This family also includes swans, most of which are larger than geese, and ducks, which are smaller.

True geese are medium to large birds, always (with the exception of the Nēnē) associated to a greater or lesser extent with water. Most species in Europe, Asia and North America are strongly migratory as wild birds, breeding in the far north and wintering much further south. However, escapes and introductions have led to resident feral populations of several species.