Religious sister (Catholic)

A religious sister in the Catholic Church is a woman who has taken public vows in a religious institute dedicated to apostolic works, as distinguished from a nun who lives a cloistered monastic life dedicated to prayer. Both nuns and sisters use the term "sister" as a form of address.

Sisters of Providence

The HarperCollins Encyclopedia of Catholicism (1995) defines as "congregations of sisters institutes of women who profess the simple vows of poverty, chastity, and obedience, live a common life, and are engaged in ministering to the needs of society."[1]:1194 As William Saunders writes: "When bound by simple vows, a woman is a sister, not a nun, and thereby called 'sister'. Nuns recite the Liturgy of the Hours or Divine Office in common ... (and) live a contemplative, cloistered life in a monastery ... behind the 'papal enclosure'. Nuns are permitted to leave the cloister only under special circumstances and with the proper permission."[2]