A rubber duck or a rubber duckie is a toy shaped like a duck, that is usually yellow with a flat base. It may be made of rubber or rubber-like material such as vinyl plastic. Rubber ducks were invented in the late 1800s when it became possible to more easily shape rubber, and are believed to improve developmental skills in children during water play.

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, since swans and geese are not considered ducks. Ducks are mostly aquatic birds, and may be found in both fresh water and sea water.