A hoax is a deliberate attempt to dupe, deceive or trick an audience into believing, or accepting, that something is real, when in fact it is not; or that something is true, when in fact it is false. In an instance of a hoax, an object, or event, is not what it appears to be, or what it is claimed to be - for example, "snake oil," which was sold by 19th century traveling salesman in the United States as a cure-all. It differs from magic in that the audience is unaware of being deceived - whereas in watching a magician perform a magical act, the audience expects to be tricked.

It is possible to perpetrate a hoax by making only true statements using unfamiliar wording or context (see Dihydrogen monoxide hoax). Unlike a fraud or con (which is usually aimed at a single victim and are made for illicit financial or material gain), a hoax is often perpetrated as a practical joke, to cause embarrassment, or to provoke social change by making people aware of something. Many hoaxes are motivated by a desire to satirize or educate by exposing the credulity of the public and the media or the absurdity of the target. For instance, the hoaxes of James Randi poke fun at believers in the paranormal and alternative medicine. The many hoaxes of Alan Abel and Joey Skaggs satirize people's willingness to believe the media. Political hoaxes are sometimes motivated by the desire to ridicule or besmirch opposing politicians or political institutions, often before elections. Journalistic scandals overlap with hoaxes to some extent.

Some governments have been known to perpetrate hoaxes to assist them with unpopular aims such as going to war (e.g., the Ems Telegram). In fact, there is often a mixture of outright hoax, and suppression and management of information to give the desired impression. In wartime, rumours abound; some may be deliberate hoaxes.

The word hoax is said to have come from the common magic incantation hocus pocus. "Hocus pocus", in turn, is commonly believed to be a distortion of "hoc est corpus" ("this is the body") from the Latin Mass.

Character of hoaxes

Hoaxes are not always created, initiated or sourced the same way. Examples:

• Hoax by tradition (see below)
• Hoax by design (such as in war)
• Hoax originating in legitimate non-hoax use (see email hoax below)
• Hoax by scare tactics (virus hoaxes)
• Urban legend

This is by no means a complete list; but the import is to show that hoaxes take many forms. The main characteristic of hoaxes is presenting the information or media as something real or believable to human understanding but is in fact false. Whether there is intent to deceive is not part of the hoax characteristics, as hoaxes are known both with and without it.

Pre-19th century

• The Donation of Constantine.
• Wolfgang von Kempelen‘s construction of the chess-playing Mechanical Turk in 1770.