Friars belong to the mendicant orders, most prominently the Franciscans, Dominicans, Carmelites and Augustinians, founded chiefly in the thirteenth century as a deliberate alternative to the older monastic pattern of stability, the vow binding a monk to remain in one monastery for life. Friars instead take vows of poverty, chastity and obedience within an order organized around mobility and active ministry, traditionally supporting themselves through begging, hence mendicant, from the Latin for begging, rather than through the landed estates and agricultural self-sufficiency that had sustained older monasteries, and directing their ministry outward toward the growing medieval cities and their populations rather than toward a settled, enclosed community life.
The distinction between a friar and a monk remains a genuine one in Catholic religious life today, though popular usage often blurs it: a friar belongs to a province of his order spanning many houses, friaries, and can be reassigned among them by his superiors in a way a stability-bound monk cannot, and his ministry, preaching, teaching, missionary work, university teaching in the case of the Dominicans and Franciscans especially, is oriented toward active engagement with the wider Church and world rather than the primarily contemplative, enclosed life monastic stability was designed to support.