§1. Societies of apostolic life resemble institutes of consecrated life; their members, without religious vows, pursue the apostolic purpose proper to the society and, leading a life in common as brothers or sisters according to their proper manner of life, strive for the perfection of charity through the observance of the constitutions.
§2. Among these are societies in which members assume the evangelical counsels by some bond defined in the constitutions.
Source: Code of Canon Law (Vatican.va)