A cardinal is a senior ecclesiastical official, usually an ordained bishop, and ecclesiastical prince of the Catholic Church. Cardinals are collectively known as the College of Cardinals, which as a body elects a new pope. The duties of the cardinals include attending the meetings of the College and making themselves available individually or in groups to the pope if he requests their counsel. Most cardinals have additional duties, such as leading a diocese or archdiocese or running a department of the Roman Curia.
A cardinal's other main function is electing the pope whenever, by death or resignation, the seat becomes vacant. In 1059, the right of electing the pope was reserved to the principal clergy of Rome and the bishops of the seven suburbicarian sees. During the sede vacante, the period between a pope's death and the election of his successor, the day-to-day governance of the Church as a whole is in the hands of the College of Cardinals. The right to enter the conclave of cardinals who elect the pope is now limited to those who have not reached the age of 80 years on the day of the pope's death or resignation.
The term cardinal at one time applied to any priest permanently assigned or incardinated to a church, or specifically to the senior priest of an important church, based on the Latin cardo (hinge), meaning "principal" or "chief". The term was applied in this sense as early as the ninth century to the priests of the tituli (parishes) of the diocese of Rome. A remnant of these earlier cardinals is retained by the Church of England, where the title of "cardinal" is still held by the two senior members of the College of Minor Canons of St Paul's Cathedral.
In the twelfth century the practice of appointing ecclesiastics from outside Rome as cardinals began, with each of them being assigned a church in Rome as his titular church, or being linked with one of the suburbicarian dioceses, while still being incardinated in a diocese other than that of Rome.