An otter is a freshwater mammal that belongs to the Mustelidae family, which also includes weasels, badgers, and wolverines. Otters are semi-aquatic animals that live in rivers, lakes, and coastal areas. They have long, slim bodies with short legs and webbed feet, and their fur is thick and waterproof. Otters are known for their playful behavior and are often seen sliding down muddy banks or playing with rocks and shells.