"Lord Bishop" is a traditional form of address used for bishops since the Middle Ages

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

, an era when bishops occupied the feudal rank of 'lord' by virtue of their office. Today it is sometimes still used in formal circumstances for any diocesan bishop in the Anglican Communion

Anglican Communion

The Anglican Communion is an international association of national and regional Anglican churches in full communion with the Church of England and specifically with its principal primate, the Archbishop of Canterbury...

 or Roman Catholic Church

Roman Catholic Church

The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...

 (except in countries, such as the United States, where this title is deemed inappropriate); it is not restricted to the 26 Church of England

Church of England

The Church of England is the officially established Christian church in England and the Mother Church of the worldwide Anglican Communion. The church considers itself within the tradition of Western Christianity and dates its formal establishment principally to the mission to England by St...

 bishops who sit in the House of Lords

House of Lords

The House of Lords is the upper house of the Parliament of the United Kingdom. Like the House of Commons, it meets in the Palace of Westminster....

 as Lords Spiritual

Lords Spiritual

The Lords Spiritual of the United Kingdom, also called Spiritual Peers, are the 26 bishops of the established Church of England who serve in the House of Lords along with the Lords Temporal. The Church of Scotland, which is Presbyterian, is not represented by spiritual peers...

. Bishops in the House of Lords are addressed as The Right Reverend Prelate the Lord Bishop of ...