The term Fourth Estate or fourth power refers to the press and news media in their explicit capacity, beyond the reporting of news, of wielding influence in politics. The derivation of the term arises from the traditional European concept of the three estates of the realm: the clergy, the nobility, and the commoners.

The equivalent term fourth power is somewhat uncommon in English, but it is used in many European languages, including German (Vierte Gewalt), Italian (quarto potere), Spanish (Cuarto poder), French (Quatrième pouvoir), Swedish (tredje statsmakten [Third Estate]), Polish (Czwarta Władza), and Russian (четвёртая власть) to refer to a government's separation of powers into legislative, executive, and judicial branches.

The expression has also been applied to lawyers, to the British Queen Consort (acting as a free agent independent of her husband), and to the proletariat. But, generally, the term Fourth Estate refers to the press and media, emphasizing its role in monitoring and influencing the other branches of government and society.

A Fifth Estate, while not recognized in the same way as the first four, includes bloggers, social media influencers, and other online platforms that can influence public discourse and politics independently of traditional media.

Oxford English Dictionary attributes ("without confirmation") the origin of the term to Edmund Burke, who may have used it in a British parliamentary debate of 19–20 February 1771, on the opening up of press reporting of the House of Commons of Great Britain. Historian Thomas Carlyle reported the phrase in his account of the night's proceedings, published in 1840, attributing it to Burke.

In modern use, the term is applied to the press, with the earliest use in this sense described by Thomas Carlyle in his book On Heroes and Hero Worship (1840): "Burke said there were Three Estates in Parliament; but, in the Reporters' Gallery yonder, there sat a Fourth Estate more important far than they all." (The three estates of the parliament of Britain were: the Lords Spiritual, the Lords Temporal and the Commons.) If Burke made the statement Carlyle associates with him, Carlyle may have had the remark in mind when he wrote in his French Revolution (1837) that "A Fourth Estate, of Able Editors, springs up; increases and multiplies, irrepressible, incalculable." In France the three estates of the Estates-General were: the church, the nobility and enfranchised townsmen.

Carlyle, however, may have mistaken his attribution: Thomas Macknight, writing in 1858, observes that Burke was merely a teller at the "illustrious nativity of the Fourth Estate". If Burke is excluded, other candidates for coining the term are Henry Brougham speaking in Parliament in 1823 or 1824 and Thomas Macaulay in an essay of 1828 reviewing Hallam's Constitutional History: "The gallery in which the reporters sit has become a fourth estate of the realm." In 1821, William Hazlitt applied the term to an individual journalist, William Cobbett, and the phrase soon became well established.

In 1891, Oscar Wilde wrote: