In modern times, the name "cardinal priest" is interpreted as meaning a cardinal who is of the order of priests. Originally, however, this referred to certain key priests of important churches of the Diocese of Rome, who were recognized as the cardinal priests, the important priests chosen by the pope to advise him in his duties as Bishop of Rome (the Latin cardo means "hinge"). Certain clerics in many dioceses at the time, not just that of Rome, were said to be the key personnel — the term gradually became exclusive to Rome to indicate those entrusted with electing the bishop of Rome, the pope.

What was the original definition of a cardinal priest?