Otter is a common name for a carnivorous mammal in subfamily Lutrinae. The 13 extant otter species are all semiaquatic or aquatic, with diets based on fish and invertebrates. Lutrinae is a branch of the weasel family Mustelidae, which also includes weasels, martens, minks, polecats, Eurasian and American badgers, honey badgers and wolverines.
A river otter is any of 13 living species of semiaquatic (or in the case of the sea otter, aquatic) mammals that feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals. An otter's den is called a holt or couch. A male otter is a meowter, a female is a queen, and a baby is a pup. The collective nouns for otters are bevy, family, lodge, or romp, (being descriptive of their often playful nature) or, when in water, raft.