Swans are large water birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the intimately related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae.
Swans typically mate for life, though "divorce" does sometimes occur, mainly following nesting failure. The number of eggs in each clutch is between 3–8.
The word is derived from Old English swan, akin to German Schwan, in turn derived from Indo-European root *swen (to sound, to sing), whence Latin derives sonus (sound). Young swans are known as cygnets, from the Latin word for swan, cygnus. An adult male is a cob, from Middle English cobbe; an adult female is a pen .