A pup is a young dog, usually less than a year old. When a dog gives birth, her babies are called pups or puppies. Pups are born with their eyes closed and depend completely on their mother for warmth and food. Within weeks, they start stumbling around, playing with their littermates, and learning about the world.

The word also applies to the young of certain other animals. Baby seals, wolves, foxes, and even sharks are called pups. Marine biologists study seal pups in their ocean colonies, and wolf pups learn hunting skills from their pack.

People sometimes use pup affectionately for any dog, even adult ones, like calling your full-grown golden retriever “good pup!” It's a warm, friendly term that captures something playful and endearing about dogs in general.