A) Consecrated life: this covers all forms of religious life, including religious institutes, secular institutes, and societies of apostolic life, as well as consecrated virgins and hermits.
B) Religious institutes: these are sisters and/or nuns that live in community and make solemn vows (also called final vows) to the evangelical virtues, e.g., Benedictines, Dominicans, and Franciscans.
C) Secular institutes: these are sisters and/or nuns that may live alone and make solemn vows, e.g., Caritas Christi, Missionaries of the Kingship of Christ, and Institut Notre Dame de Vie.
D) Societies of Apostolic Life: these are sisters that typically live in community and make simple promises or some other kind of bond, depending on the nature of the society. They are different from religious and secular institutes, insofar as they are more focused on the mission of their society rather than the institute itself, e.g., Society of Our Lady of the Most Holy Trinity (SOLT), Society of the Holy Child Jesus, and Society of the Catholic Apostolate (Pallotines).
E) Sisters or Nuns? The term “nun” technically refers to sisters that live a cloistered life. In other words, nuns that live in the cloister usually do not step outside their convent or monastery unless health requires it. The term “sister” then, technically refers to sisters who are not cloistered. Both nuns and sisters are addressed as “Sister” when spoken to, but the terms are used when referring to what kind of community they belong to, e.g. “Those are the Poor Clare nuns that live at St. Francis Monastery.” And, “Hello, Sister Maria!”