This is a phrase that refers to the profession of Journalism, specifically the Press.
It is derived from the old English idea that there are three estates:
1. the Lords Spritual – those members of the clergy, mainly Bishops, who are members of the House of Lords.
According to the UK Parliament website:
“… until the Reformation,the Lords Spiritual made up the majority of members of the House of Lords. They included archbishops, bishops and mitred abbots.
However, with the dissolution of the monasteries in the 16th century, there were no abbots to attend, and with limitations being placed on the number of bishops entitled to sit in the Lords, the number of spiritual peers is now reduced to 26. They include the Archbishops of Canterbury and York, the Bishops of Durham, London and Winchester, and the 21 next most senior Church of England Bishops.”
2. the Lords Temporal – those members of the House of Lords who are either hereditary peers, Law Lords, or Lords appointed for life.
The UK Parliament website says:
“Since the House of Lords Act 1999, only 92 hereditary peers remain, 75 of whom were elected by their respective party groups. The remaining 17 are office holders or have ceremonial offices.”
3. the House of Commons – the lower house, or “people’s house” of the British Parliament, now the seat of government.
The notion that the Press is the fourth estate rests on the idea that the media’s function is to act as a guardian of the public interest and as a watchdog on the activities of government.
Depending on one’s view of the media, this is either self-serving rationalisation, or an important component of the checks and balances that form part of a modern democracy.