Enclosed religious orders of the Christian church have solemn vows with a strict separation from the affairs of the external world. The term cloistered is synonymous with enclosed. The "enclosure" is regulated by Catholic church law, The Code of Canon Law, Canon 667 ff. English translation copyright 1983 The Canon Law Society Trust and prevents members from going out of the religious house, and also prevents strangers from entering the monastery, convent or abbey. The stated purpose for such enclosure is to prevent distraction from prayer and the religious life. The ecclesiastical penalties for disobeying the rules of enclosure include excommunication.

Enclosed orders of men include the Cistercians and the Carthusians and enclosed orders of women include the Augustinian nuns, and some convents of Dominican nuns, Carthusian nuns, Ursulines, Carmelites, and Tyburn nuns.

The English word monk most properly refers to men in monastic life, while the term friar more properly refers to mendicants active in the broader world (like Franciscans, Dominicans and Augustinians), though not all monasteries require strict enclosure (Benedictines have often staffed parishes and been allowed to leave monastery confines). Although the English word nun is often used to describe Christian women who have joined religious orders, strictly speaking, female church members are referred to as nuns only when they live in enclosure, otherwise they are "sisters". The distinctions between the Christian terms monk, nun, friar, brother, and sister are sometimes easily blurred because some orders (such as the Dominicans or Augustinians) include nuns (who are enclosed) and sisters (who work in the broader world).