User:Whinney

A Catholic nun or sister is a woman who has professed vows of poverty, chastity, and obedience within the Roman Catholic Church. The terms nun and sister are often used interchangeably, however there are canonical differences in the type of vows that the women profess. Also, though the two terms once signified different ways of living (nuns tended to lead a cloistered life of prayer and meditation; sisters tended to lead an active life in service to people in need), these distinctions now serve as generalizations but do not accurately reflect the reality of religious life in the early 21st century.

titles for the leader of the religious community
mother superior, superior general, general superior, mother general, president, congregational leader, abbess, prioress

How to address a Catholic nun or sister
Sister, Mother, Reverend Mother,