Answer: A monk is one who has bound himself to the monastic life by taking vows in its integrity. In the Eastern churches all religious are monks; in the Western church, only the members of the following orders: the Benedictine, Carmeldolese, Vollombrosan, Sylvertrine, Olivetan, Cistercian, and Carthusian. Canons regular are sometimes referred to as monks; but the distinction between a monk and a friar is very sharp, both in law and in fact.
A friar is a member of one of the so-called mendicant orders. “Friar” is not synonymous with “Monk,” they are as different as artillery is from infantry. The life of a monk is normally passed within the walls of a monastery; a friar has his headquarters in a friary but his work is of the active ministry and may take him to all parts of the earth; a friar is a member of a highly organized, widespread body with a central authority to which he is professed; a monk’s allegiance is to the abbot of an autonomous individual monastery. Moreover, these is no limit as to the amount of property which monks may hold as a corporation; originally friars might have none, even in common, but this was modified by the Council of Trent. The four mendicant orders of the common law are the Dominicans, Franciscans, Carmelites, and Augustinians; the lesser friars are the Servites, Trinitarians, Mercedarians, Hieronymites, Minims, Brothers of Saint John od God, and the Oder of Penitents.