A hoax (plural: hoaxes) is a widely publicised falsehood created to deceive its audience with false and often astonishing information, with the either malicious or humorous intent of causing shock and interest in as many people as possible.

Some hoaxers intend to eventually unmask their representations as having been a hoax so as to expose their victims as fools; seeking some form of profit, other hoaxers hope to maintain the hoax indefinitely, so that it is only when skeptical people willing to investigate their claims publish their findings, that the hoaxers are finally revealed as such.

Zhang Yingyu's The Book of Swindles (c. 1617), published during the late Ming dynasty, is said to be China's first collection of stories about fraud, swindles, hoaxes, and other forms of deception. Although practical jokes have likely existed for thousands of years, one of the earliest recorded hoaxes in Western history was the drummer of Tedworth in 1661. The communication of hoaxes can be accomplished in almost any manner that a fictional story can be communicated: in person, via word of mouth, via words printed on paper, and so on. As communications technology has advanced, the speed at which hoaxes spread has also advanced: a rumour about a ghostly drummer, spread by word of mouth, will affect a relatively small area at first, then grow gradually. However, hoaxes could also be spread via chain letters, which became easier as the cost of mailing a letter dropped. The invention of the printing press in the 15th century brought down the cost of a mass-produced books and pamphlets, and the rotary printing press of the 19th century reduced the price even further (see yellow journalism). During the 20th century, the hoax found a mass market in the form of supermarket tabloids, and by the 21st century there were fake news websites which spread hoaxes via social networking websites (in addition to the use of email for a modern type of chain letter).

The English philologist Robert Nares (1753–1829) says that the word hoax was coined in the late 18th century as a contraction of the verb hocus, which means "to cheat", "to impose upon" or (according to Merriam-Webster) "to befuddle often with drugged liquor." Hocus is a shortening of the magic incantation hocus pocus, whose origin is disputed.^{[better source needed]}

Robert Nares defined the word hoax as meaning "to cheat", dating from Thomas Ady's 1656 book A candle in the dark, or a treatise on the nature of witches and witchcraft.

The term hoax is occasionally used in reference to urban legends and rumours, but the folklorist Jan Harold Brunvand argues that most of them lack evidence of deliberate creations of falsehood and are passed along in good faith by believers or as jokes, so the term should be used for only those with a probable conscious attempt to deceive. As for the closely related terms practical joke and prank, Brunvand states that although there are instances where they overlap, hoax tends to indicate "relatively complex and large-scale fabrications" and includes deceptions that go beyond the merely playful and "cause material loss or harm to the victim."

According to Professor Lynda Walsh of the University of Nevada, Reno, some hoaxes – such as the Great Stock Exchange Fraud of 1814, labelled as a hoax by contemporary commentators – are financial in nature, and successful hoaxers – such as P. T. Barnum, whose Fiji mermaid contributed to his wealth – often acquire monetary gain or fame through their fabrications, so the distinction between hoax and fraud is not necessarily clear. Alex Boese, the creator of the Museum of Hoaxes, states that the only distinction between them is the reaction of the public, because a fraud can be classified as a hoax when its method of acquiring financial gain creates a broad public impact or captures the imagination of the masses.

One of the earliest recorded media hoaxes is a fake almanac published by Jonathan Swift under the pseudonym of Isaac Bickerstaff in 1708. Swift predicted the death of John Partridge, one of the leading astrologers in England at that time, in the almanac and later issued an elegy on the day Partridge was supposed to have died. Partridge's reputation was damaged as a result and his astrological almanac was not published for the next six years.