Original: Several other small, elongated carnivorous mammals belonging to the family Mustelidae (weasels) also have the word ferret in their common names, including an endangered species, the Black-footed Ferret.
Simplified: A ferret, the domestic ferret (Mustela putorius furo), is a small animal from the Mustelidae family. Several other Mustelids have the word "ferret" in their name, but they are not the same.