Geese are waterfowl belonging to the tribe Anserini of the family Anatidae. This tribe comprises the genera Anser (the grey geese), Branta (the black geese) and Chen (the white geese). A number of other birds, mostly related to the shelducks, have "goose" as part of their name. More distantly related members of the Anatidae family are swans, most of which are larger than true geese, and ducks, which are smaller.The word goose is a direct descendant of Proto-Indo-European root, *ghans-. In Germanic languages, the root gave Old English gōs with the plural gēs and gandres (becoming Modern English goose, geese, and gander, respectively), New High German Gans, Gänse, and Ganter, and Old Norse gās. This term also gave Lithuanian žąsìs, Irish gé (goose, from Old Irish géiss), Latin anser, Greek χήν/khēn, Albanian gatë (heron), Sanskrit hamsī, Finnish hanhi, Avestan zāō, Polish gęś, Russian гусь, Czech husa, and Persian ghāz.
The term goose applies to the female in particular while gander applies to the male in particular. Young birds before fledging are called goslings. The collective noun for group of geese on the ground is a gaggle; when in flight, they are called a skein, a team or a wedge; when flying close together, they are called a plump.There are three living genera of true geese: Anser, grey geese, including the domesticated goose and the Swan Goose; Chen, white geese (often included in Anser); and Branta, black geese, such as the Canada goose.
Two genera of "geese" are only tentatively placed in the Anserinae; they may belong to the shelducks or form a subfamily on their own: Cereopsis, the Cape Barren Goose, and Cnemiornis, the prehistoric New Zealand Goose.
Either these or, more probably, the goose-like Coscoroba Swan is the closest living relative of the true geese.
Fossils of true geese are hard to assign to genus; all that can be said is that their fossil record, particularly in North America, is dense and comprehensively documents many different species of true geese that have been around since about 10 million years ago in the Miocene. The aptly named Anser atavus (meaning "Great-great-great-grandfather goose") from some 12 million years ago had even more plesiomorphies in common with swans. In addition, there are some goose-like birds known from subfossil remains found on the Hawaiian Islands.