From The TV IV
A MacGuffin (also spelled McGuffin or Maguffin) is a plot device which advances the story but which is itself secondary to the development of the plot. It can be a person, a quest or an object. A MacGuffin is distinguished from other plot devices in that, by definition, the actual item which a MacGuffin is could be interchangeable with other, similar plot devices. For instance, almost every season of 24 involves a MacGuffin of some type or another in the form of a terrorist threat. That threat may be a nuclear bomb, a form of biological warfare or a poison gas, but one of those terrorist threats could easily be exchanged for any other terrorist threat (i.e.: In Season Two, it could just as easily have been a biological weapon which the terrorists confiscated and not a nuclear bomb), and the development of the story could have remained more or less unchanged. Further, MacGuffins frequently prove to be "shaggy dog stories"—in other words, they may prove to be nothing at all—as with the supposed bacteria smuggled into the country by a teenager in Season Three of 24.
Filmmaker and director Alfred Hitchcock is credited with having popularized the term. (Some sources credit him as having coining it, as well, although other sources credit its coinage to Hitchcock's friend, screenwriter Angus MacPhail.) He has also been credited with popularizing the usage of the MacGuffin in storytelling, in that almost all of his classic films involve a MacGuffin of some sort or another (the embezzled funds in Psycho; the broken leg in Rear Window; the painting in Vertigo; the uranium in Notorious; the government secrets in North by Northwest; etc.). In response to its origin, the Master of Suspense (and often Master of Dry Wit) told a story regarding two Scottish men on a train, of whom one had a package in the baggage rack. When the second man asked the first man what was in the package, the first man replied, "A MacGuffin," which he said was "an apparatus for trapping lions in the Scottish Highlands." The second man objects that there are no lions in the Highlands, to which the first man responds, "Well, then that's no MacGuffin!" In other stories and interviews, Hitchcock gave other definitions for the term. In one of these definitions, he repeated T.S. Eliot's description of the "meaning" of a poem: "The bone thrown by a burglar to distract the watchdog of the mind while the poem goes about its own, deeper business."
Hitch may not have been the first to use a MacGuffin, but it is interesting to note that the concept seems to appear only rarely much prior to the twentieth century—and those classical uses of the MacGuffin seem to use it unintentionally. Further, the MacGuffin as a storytelling tool became more prevalent with the popularization of the mystery and suspense genres, although its usage would eventually spill over into all generic types of stories—Westerns, science fiction, etc. In fact, one of the greatest pre-20th century known examples of a MacGuffin is the titular object in the short story "The Purloined Letter" by Edgar Allan Poe, who is often credited as the inventor of the detective genre.
As a result, MacGuffins play a significant role in 20th- and 21st-century literature. Author Raymond Chandler frequently employed them in his Philip Marlowe stories, as did Dashiell Hammet (who, like Poe, made his MacGuffin the title of one of his most famous novels, The Maltese Falcon). George Orwell uses a MacGuffin in the form of Room 101 and its horrors in 1984. The ring is a MacGuffin in J.R.R. Tolkien's The Lord of the Rings, as is Ice-Nine in Kurt Vonnegut's Cat's Cradle. In film, MacGuffins were not limited to Hitchcock's body of work. Such other directors as Orson Welles (Rosebud in Citizen Kane; the police reports in Touch of Evil), Stanley Kubrick (the abort code in Dr. Strangelove; the Beethoven music in A Clockwork Orange; the mask in Eyes Wide Shut) and Quentin Tarantino (the diamonds in Reservoir Dogs; the briefcase in Pulp Fiction; the "five point palm exploding heart technique" in Kill Bill) utilized MacGuffins to great effect.
In television, MacGuffins have been used since the dawn of television. Of course, Hitchcock himself often employed them in Alfred Hitchcock Presents, as did Rod Serling on many episodes of The Twilight Zone and Night Gallery. In episodics, they often present themselves in one of two ways: The first is the use of one or more MacGuffins over the course of a season (as with 24) or a mystery/monster/premise in each episode (the X File of the week on The X Files, the monster of the week on Buffy the Vampire Slayer, the mystery of the week on Veronica Mars or The Rockford Files, the medical mystery of the week on House, M.D.), which exists largely to propel the character drama of the series or season. The second is the mystery or hook set up in the pilot (the beast on the island in Lost, the murder of Laura Palmer on Twin Peaks, the Adena Watson case on Homicide: Life on the Street, the organization of Prophet 5 on Alias, the future mother on How I Met Your Mother), which exists primarily to hook both the network and the audience on the premise of a show. In the latter case, the MacGuffin of the pilot is frequently dropped as the series continues.