Goose (plural: geese) is the 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.
A number of other waterbirds, mainly related to the shelducks, have "goose" as part of their name.
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 farther south. However, escapes and introductions have led to resident feral populations of several species.
All geese eat a vegetarian diet, and can become pests when flocks feed on arable crops or inhabit ponds or grassy areas in urban environments. They also take invertebrates if the opportunity presents itself; domestic geese will try out most novel food items for edibility.
Geese usually mate for life, though a small number will "divorce" and remate. They tend to lay a smaller number of eggs than ducks but both parents protect the nest and young, which usually results in a higher survival rate for the young geese.
Not all couples are heterosexual, as both females and males will form long-term same-sex couples with greater or lesser frequency depending on species. Of the homosexual couples, a significant proportion are non-breeding despite having an active sexual life.
Goose in its origins is one of the oldest words of the Indo-European languages (Crystal), the modern names deriving from the proto-Indo-European root, ghans, hence Sanskrit hamsa (feminine hamsii), Latin anser, Greek khén etc.
In the Germanic languages, the root word led to Old English gos with the plural gés, German Gans and Old Norse gas. Other modern derivatives are Russian gus and Old Irish géiss; the family name of the cleric Jan Hus is derived from the Czech derivative husa.
The male goose is called a gander (Anglo-Saxon gandra) and the female is the goose (Webster's Revised Unabridged Dictionary (1913)); young birds before fledging are known as goslings. A group of geese on the ground is called a gaggle; when flying in formation, it is called a wedge or a skein (see also list of collective nouns for birds).
The following two genera are only tentatively placed in the Anserinae; they may belong to the shelducks or form a subfamily on their own:
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 a lot of the different species of true geese that have been around since about 10 million years ago in the Miocene. The aptly-named Anser atavus ("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. See Anserinae for more.
The Blue-winged Goose, Cyanochen cyanopterus belongs either to these, or to lineage closer to ducks.
The three species of small waterfowl in the genus Nettapus are named "pygmy geese", e.g. the Cotton Pygmy Goose (N. javanica). They seem to represent an ancient lineage like the Cape Barren Goose and the Spur-winged Goose.
The unusual Magpie-goose is in a family of its own, the Anseranatidae.