The convents of friars were not independent bodies, like the Benedictine and Augustinian abbeys; each order was an organised body, governed by the general of the order, and under him, by provincial priors, priors of the convents, and their subordinate officials. There are usually reckoned four orders of friars—the Dominicans, Franciscans, Carmelites, and Augustines.
“I found there freres,
All the foure orders,
Techynge the peple
To profit of themselves.”
Piers Ploughman, l. 115.
The four orders are pictured together in the woodcut page from the thirteenth century MS. Harl. 1,527.
They were called Friars because, out of humility, their founders would not have them called Father and Dominus, like the monks, but simply Brother (Frater, Frère, Friar).