(Nerd)
Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form taxon; they do not represent a monophyletic group (the group of all descendants of a single common ancestral species), since swans and geese are not considered ducks. Ducks are mostly aquatic birds, and may be found in both fresh water and sea water. Ducks are sometimes confused with several types of unrelated water birds with similar forms, such as loons or divers, grebes, gallinules and coots.

Ducks have a cosmopolitan distribution, and are found on every continent except Antarctica. Several species manage to live on subantarctic islands, including South Georgia and the Auckland Islands. Ducks have reached a number of isolated oceanic islands, including the Hawaiian Islands, Micronesia and the Galápagos Islands, where they are often vagrants and less often residents. A handful are endemic to such far-flung islands. Some duck species, mainly those breeding in the temperate and Arctic Northern Hemisphere, are migratory; those in the tropics are generally not. Some ducks, particularly in Australia where rainfall is erratic, are nomadic, seeking out the temporary lakes and pools that form after localised heavy rain.

(English)
Ducks are birds in the family Anatidae. Ducks are closely related to swans and geese, which are in the same family. Ducks are not a monophyletic group. They are a ‘form taxon’. Swans and geese are in the same family but are not called ducks. The main difference is that ducks have shorter necks, and are smaller.