From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) The church and palace of St. John Lateran, the church being the cathedral church of Rome, and the highest in rank of all churches in the Catholic world.

The Nuttall Encyclopedia [2]

The palace, originally a basilica, built by Constantine in Rome about 333, the residence of the Pope till 1308, and from which no fewer than five Ecumenical Councils receive their names as held in it, namely, those of 1123,1139, 1179,1215, and 1518; the church, called the Church of St. John Lateran, is the cathedral church of Rome.