Within the clerical hierarchy of the Catholic Church, there are really three levels: deacons, priests, and bishops. Among bishops there are several varieties: bishops, archbishops, and cardinals. The pope is, of course, a bishop: the bishop of Rome. But beneath the pope in the hierarchy are the cardinals: bishops or archbishops of higher rank. Although they have special responsibilities and greater prominence in the universal Church, cardinals have no increased regional jurisdiction; although they are influential, their actual sphere of responsibility is generally within their own diocese or archdiocese.
Many people think that cardinals are named for their distinctive red dress. In fact, it’s the other way around. The red vesture (and the bright red bird called a cardinal) is named for the ecclesial office. The word “cardinal” comes from the Latin word “cardo,” which means “hinge,” or that on which another thing depends. Their red clothing became customary after the pope Innocent IV in 1245, and was to be a reminder that the cardinals should be ready to lay down their lives for the Gospel. Customarily, cardinals serve the catholic faithful in large cities including New York, Boston, Washington DC, Chicago, Detroit and Los Angeles.
In the year 1590 the cardinals were given the responsibility of electing a new pope, when that becomes necessary. Up to 120 cardinals under the age of 80 are eligible to vote for the next pope.