Metasyntactic Variable

A Metasyntactic Variable -- also called a "Placeholder Name" -- is a word or phrase used in the place of another word or phrase in any of several contexts. By mathematical analogy, a metasyntactic variable is a word that is a variable for other words, just as in algebra letters are used as variables for numbers.

In computing and technology contexts, these words are commonly found in source code and are intended to be modified or substituted before real-world usage. The words foo and bar are good examples as they are used in over 330 Internet Engineering Task Force Requests for Comments, the documents which define foundational internet technologies like HTTP (websites), TCP/IP, and email protocols. Metasyntactic variables are used to name entities such as variables, functions, and commands whose exact identity is unimportant and serve only to demonstrate a concept, which is useful for teaching programming. A short examination of Metasyntactic Variables as used in computing can be found at the Coding Horror blog.

Outside of computing contexts, these are words that functional grammatically as nouns and that can refer to objects, places or people whose names do not exist, are temporarily forgotten, irrelevant, or unknown in the context in which they are being discussed. This can include such terms as "watchamacallit", "thingamabob", "dojiggy" and "wossname" (the latter being primarily a UK usage), or a term as simple as "thing". Most of these words can be documented to least the 19th century.

Some fields have their own specific placeholder terminology. For example, "widget" in economics, engineering and electronics, or "Blackacre" and "John Doe" or "Jane Doe" in law.

Advertising

 * "Brand X" is used in television advertisements as a generic brand representing any other brand than the one being advertised.

Fan Works

 * Can be found at play twice in the title of the Harry Potter/Doctor Who Crossover fic Potter Who and the Wossname's Thingummy.

Film

 * Fictional brands such as Morley are often used in film and television as placeholders to avoid unintended Product Placement.

Literature

 * Edgar Allan Poe wrote a short story entitled "The Literary Life of Thingum Bob, Esq.", showing that particular form to be in familiar use in the United States in the 1840s.

Live-Action TV

 * The "X" in the title of The X-Files is a Metasyntactic Variable referring to the unknown and possibly paranormal aspects of the cases within those files.
 * "Oceanic Airlines" -- most famously seen in Lost -- is used as a "placeholder" fictional airline in films, TV program, and comic books, typically when a plane is involved in a disaster or another event with which actual airlines would prefer not to be associated.

Theatre
"... apologetic statesmen of a compromising kind, Such as: What d'ye call him: Thing'em-bob, and likewise: Never-mind, and 'St: 'st: 'st: and What's-his-name, and also You-know-who: The task of filling up the blanks I'd rather leave to you."
 * In Gilbert and Sullivan's The Mikado, W. S. Gilbert makes the Lord High Executioner sing of a "little list" which includes:

Web Original

 * The Jargon File has an extensive entry on the subject that documents not just American and British usage but terms used by programmers from continental Europe and New Zealand.

Real Life

 * Metasyntactic variables used commonly across all programming languages include foobar, foo, bar, baz, qux, quux, quuz, corge, grault, garply, waldo, fred, plugh, xyzzy, and thud; several of these words are references to the game Colossal Cave Adventure.
 * Wibble, wobble, wubble, and flob are also used in the UK.
 * Japanese programmers commonly use hoge (ほげ)[5] and piyo (ぴよ), with other common words and variants being fuga (ふが), hogera (ほげら), and hogehoge (ほげほげ).
 * In France, the word toto is widely used by programmers, with variants tata, titi, and tutu as related placeholders.
 * The Whatchamacallit bar, a chocolate/peanut butter/caramel candy bar introduced by Hershey in 1978, uses a Metasyntactic Variable as its name to emphasize what at the time of its release was a candy bar allegedly radically different from any produced before.
 * Hershey also briefly (2009-2012) produced a chocolate-peanut butter bar called the Thingamajig.
 * "X-ray" was originally a placeholder name for an unexplained phenomenon, with "X" representing, as in algebra, the unknown.
 * It is common to use the name ACME in example SQL Databases and as placeholder company-name for the purpose of teaching. The term 'ACME Database' is commonly used to mean a training or example-only set of database data used solely for training or testing. ACME is also commonly used in documentation which shows SQL usage examples, a common practice with in many educational texts as well as technical documentation from companies such as Microsoft and Oracle.
 * "Advent corporation" is a term used by lawyers to describe an as yet unnamed corporation, while legal incorporation documents are being prepared.
 * The very real Advent Corporation (active 1967-1981) got its name when its founder liked the sound of the placeholder.