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.

Kraal is an Afrikaans and Dutch word, also used in South African English, for an enclosure for cattle or other livestock, located within a Southern African settlement or village surrounded by a fence of thorn-bush branches, a palisade, mud wall, or other fencing, roughly circular in form. It is similar to a boma in eastern or central Africa.