A patron saint is the saint who gives protection to groups or individuals, usually because of a shared name or activity. Thus, Saints Cosmas and Damian, doctors, were the patron saints of the Medici (Italian for doctors) family of Florence; Saint Christopher became the patron saint of travellers because according to legend he carried the infant Christ across a river.
Towns and cities also had their patron saints, as did the guilds and confraternities. The patron saints of the great religious orders were of course their founders, such as Saint Benedict and Saint Dominic.