Consecrated life may be lived either individually or as a member of an institute. The Catholic Church recognises, as forms of individual consecrated life, that of a hermit and that of a consecrated virgin. It also envisages new forms of consecrated life emerging. Religious institutes are one of the two types of institutes of consecrated life. The other is that of the secular institute, defined as "an institute of consecrated life in which the Christian faithful, living in the world, strive for the perfection of charity and seek to contribute to the sanctification of the world, especially from within".
Societies of apostolic life resemble religious institutes, but differ in that their members do not take religious vows. They pursue the apostolic purpose of the society to which they belong, while leading a life in common as brothers or sisters and striving for the perfection of charity through observing the society's constitutions. In some of these societies the members assume the evangelical counsels by a bond other than that of religious vows defined in their constitutions.
Since each and every religious institute has its own unique aim, or charism, it has to adhere to a particular way of religious living that is conducive to it, whether "contemplative", "enclosed", mendicant, or apostolic. Thus some religious institutes – especially of nuns who are subject to "Papal Enclosure" – strictly isolate their members from the outside world, of which the "grilles" in their parlours and churches are tangible evidence. Other religious institutes have apostolates that require their members to interact practically with the secular world, such as teaching, medical work, producing religious artworks and texts, designing and making vestments and writing religious instruction books, while maintaining their distinctiveness in communal living. Several founders, in view of their aim, require the members of their institute not only to profess the three Evangelical Counsels of chastity, poverty, obedience, but also to vow or promise stability or loyalty, and maybe certain disciplines, such as self-denial, fasting, silence.
Religious orders are subdivided as:
Traditionally, institutes for men are referred to as the "First Orders" and those of women as the "Second Orders". Some religious orders, for example the Franciscans or the Dominicans, have "Third Orders" of associated religious members who live in community and follow a rule (called Third Order Religious or TOR), or lay members who, without living in formal community with the order, have made a private vow or promise to it, such as of perseverance in pious life, hence are not "religious", that is to say, not members of the Consecrated life (often called Third Order Secular, or TOS).