Duck is the common name for numerous species in the waterfowl family Anatidae which also includes swans and geese. Ducks are divided among several subfamilies in the family Anatidae; they do not represent a monophyletic group (the group of all descendants of a single common ancestral species) but a form taxon, since swans and geese are not considered ducks. Ducks are mostly aquatic birds, mostly smaller than the swans and geese, and may be found in both fresh water and sea water.
Here, have a picture of a duck :)
Ducks are very important for wetlands/marshland. They create and renew habitats just by going about their daily lifestyle! They forage during the night, and during this foraging they eat many seeds and fruit, and then this helps with seed dispersal. And when the seeds grow, all different species of small animal can live in the plants!