The state of people who profess to aim at the perfection of Christian charity in the bosom of the Church, by the three perpetual vows of poverty, chastity, and obedience.
The religious life pointed out to us by the Evangelical counsels is a life of charity and of union with God, and the great means it employs to this end are freedom and detachment from everything that could in any manner prevent or impair that union.
From another point of view it is a devotion, a special consecration to Christ and God, to whom every Christian acknowledges that he belongs.
Christian virgins were the first to profess a life distinguished from the ordinary, by its tendency to perfection; continence, and often the renunciation of riches, attached them specially to Christ.
Shortly after them, appeared the "confessores" who also made profession of chastity and sometimes of poverty.
In the 3rd century we find the first distinct traces of the kind of life in which the religious profession becomes by degrees perfected and brought under rule, that of the monks.
The Gospel clearly states virginity and continence as the means, and charity as the end, of all religious life.
Persecutions necessitated retirement and a first form of life entirely directed towards personal sanctification; community life produced obedience; the inconveniences caused by frequent changes of residence suggested the vow of stability; the excessive multiplication and diversity of religious institutes called for the intervention of the sovereign pontiff and his express approbation of rules; the needs of soul and body grafted the practise of corporal and spiritual works of mercy upon personal sanctification, and joined the reception of Holy Orders to religious profession; and the exigencies and difficulties of modern times caused the making of simple vows antecedent to, or in substitution for, solemn vows.
Some examples of the regular religious life may be seen among the Canons Regular, the mendicant orders, the military orders, the hospitaller orders, the Clerks Regular, the Eastern orders, those orders founded principally for teaching, as the Christian Brothers, and innumerable congregations of nuns.
New Catholic Dictionary