A pen is an enclosure for holding livestock. It may also perhaps be used as a term for an enclosure for other animals such as pets that are unwanted inside the house. The term describes types of enclosures that may confine one or many animals. Construction and terminology vary depending on the region of the world, purpose, animal species to be confined, local materials used and tradition. Pen or penning as a verb refers to the act of confining animals in an enclosure.

A dog crate, dog cage, or kennel is a metal, wire, plastic, or fabric enclosure with a door in which a dog may be kept for security or transportation. Dog crates are designed to replicate a dog's natural den and as such can provide them with a place of refuge at home or when traveling to new surroundings. Other common reasons for using a dog crate are for toilet training a new puppy, transporting a dog, limiting access while the dog learns rules, ensuring the dog's safety, confining a dog in locations where dogs cannot safely or legally roam freely, or giving a dog a place to go when visitors come to the house.