Nuns in different parts of the world
A nun is a member of a religious community of women, typically one living under vows of poverty, chastity, and obedience. She may have decided to dedicate her life to serving all other living beings, or she might be an ascetic who voluntarily chose to leave mainstream society and live her life in prayer and contemplation in a monastery or convent. The term "nun" is applicable to Catholics (eastern and western traditions), Orthodox Christians, Anglicans, Lutherans, Jains, Buddhists, Taoists, Hindus and some other religious traditions.
While in common usage the terms "nun" and "sister" are often used interchangeably (the same title of "Sister" for an individual member of both forms), they are considered different ways of life, with a "nun" being a religious woman who lives a contemplative and cloistered life of meditation and prayer for the salvation of others, while a "religious sister", in religious institutes like St. Mother Teresa's Missionaries of Charity, lives an active vocation of both prayer and service, often to the needy, ill, poor, and uneducated.