• The term Fourth Estate or fourth power refers to the press and news media both in explicit capacity of advocacy and implicit ability to frame political issues.
• Though it is not formally recognized as a part of a political system, it wields significant indirect social influence.
• The Fourth Estate is a societal power, force or institution whose influence is not consistently or officially recognised as such. ‘Fourth Estate’ most commonly refers to the news media, journalism or ‘the press’.
• The term ‘Fourth Estate’ makes implicit reference to the earlier historical division of the Three Estates of the Realm: the clergy, the nobility, and the commoners.
• The equivalent term ‘fourth power’, used in many European languages as it historically belongs to European constitutional lore dating back to the time of the Roman Empire, refers to the separation of powers into legislative, executive and judiciary branches.
• This separation of power has become the construct upon which nations have been built throughout the world. Of which the press is the fourth element.

Source: ForumIAS