A nun is a woman who has dedicated her life to religious service and contemplation, typically living under vows of poverty, chastity, and obedience in the enclosure of a monastery or convent. Although the usage of the term has varied throughout church history, typically "nun" is used for women who have taken "solemn" vows, and "sister" is used for women who have taken "simple" vows (that is, vows other than solemn vows) . A Catholic nun is a woman who lives as a contemplative life in a monastery which is usually cloistered (or enclosed) or semi-cloistered. Her ministry and prayer life is centered within and around the monastery for the good of the world. She professes the perpetual solemn vows living a life according to the evangelical counsels of poverty, celibacy, and obedience. On the other hand, a Catholic sister is a woman who lives, ministers, and prays within the world. A sisters life is often called "active" or "apostolic" because she is engaged in the works of mercy and other ministries that take the Gospel to others where they are. She professes perpetual simple vows living a life according to the evangelical counsels of poverty, celibacy, and obedience. The term "nun" is also used to refer to various birds, especially a domestic variety.