Christian nuns

A nun is a woman who vows to dedicate her life to religious service and contemplation, typically living under vows of poverty, chastity, and obedience in the enclosure of a monastery or convent. The term is often used interchangeably with religious sisters, who do take simple vows but live an active vocation of prayer and charitable work in the wider society.

early Christian ascetics, 3rd–5th centuries AD

Apostolic constitution of Pope Francis

In the 1st century AD, the Agapetae (from the Greek word ἀγαπηταί (agapetai), meaning 'beloved') were virgins who consecrated themselves to God with a vow of chastity and associated with laymen.