These placeholders typically function grammatically as nouns and can be used for people (e.g. John Doe, Jane Doe), objects (e.g. widget), locations ("Main Street"), or places (e.g. Anytown, USA). They share a property with pronouns, because their referents must be supplied by context; but, unlike a pronoun, they may be used with no referent—the important part of the communication is not the thing nominally referred to by the placeholder, but the context in which the placeholder occurs.
In their Dictionary of American Slang (1960), Stuart Berg Flexner and Harold Wentworth use the term kadigan for placeholder words. They define "kadigan" as a synonym for thingamajig. The term may have originated with Willard R. Espy, though others, such as David Annis, also used it (or cadigans) in their writing. Its etymology is obscure—Flexner and Wentworth related it to the generic word gin for engine (as in the cotton gin). It may also relate to the IrishsurnameCadigan. Hypernyms (words for generic categories; e.g., "flower" for tulips and roses) may also be used in this function of a placeholder, but they are not considered to be kadigans.
Placeholder words exist in a highly informal register of the English language. In formal speech and writing, words like accessory, paraphernalia, artifact, instrument, or utensil are preferred; these words serve substantially the same function, but differ in connotation.
Most of these words can be documented in at least the 19th century. 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. In Gilbert and Sullivan's The Mikado, W. S. Gilbert makes the Lord High Executioner sing of a "little list" which includes:
... 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.
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. "X-ray" was originally a placeholder name for an unexplained phenomenon.
Companies and organizations
"Ace" and "Acme" were popular in company names as positioning words in alphabetical directories. They were generic, laudatory of whatever products they were used to promote and appeared at the beginning of most alpha-sorted lists. The Acme Corporation of cartoon fame is one placeholder example. (Acme is a regular English word from the Ancient Greekἀκμή, akme meaning summit, highest point, extremity or peak, and thus sometimes used for "best".)
"Mom and Pop" (in the United States) are occasional placeholders for the individual owners of a generic, very small family business
"Advent corporation" is a term used by lawyers to describe an as yet unnamed corporation, while legal incorporation documents are being prepared. In the case of Advent Corporation, founder Henry Kloss decided to adopt this placeholder name as the formal legal name of his new company.
"NewCo" or "Newco" is used in a similar way in British English for an as-yet-unnamed company.
"XYZ Widget Company" has long been used in business and economics textbooks as a sample company. Also used as engraving text example on items such as plaques, trophy plates, etc. Occasionally appears on customizable promotional materials including stationery templates, business cards, advertising signage, cups, backpacks, and other "swag" samples.
Foo, Bar, Baz, and Qux (and combinations thereof) are commonly used as placeholders for file, function and variable names. Foo and bar are derived from foobar.
Hacker slang includes a number of placeholders, such as frob which may stand for any small piece of equipment. To frob, likewise, means to do something to something. In practice it means to adjust (a device) in an aimless way.
Alice and Bob, alternatives for 'Person A'/'Person B' when describing processes in telecommunications; in cryptography Eve (the eavesdropper) is also added.
J. Random X (e.g. J. Random Hacker, J. Random User) is a term used in computer jargon for a randomly selected member of a set, such as the set of all users. Sometimes used as J. Random Loser for any not-very-computer-literate user.
Johnny/Jane Appleseed, commonly used as a placeholder name by Apple.
Contoso is a fictional company name commonly used as an example in Microsoft documentation.
Certain domain names in the format example.tld (such as example.com, example.net, and example.org) are officially reserved as placeholders for the purpose of presentation. Various example reserved IP addresses exist in IPv4 and IPv6, such as 192.0.2.0 in IPv4 documentation and 2001:db8:: in IPv6 documentation.
Placeholders such as Main Street, Your County, and Anytown are often used in sample mailing addresses. Ruritania is commonly used as a placeholder country.
Timbuktu, which is also a real city, is often used to mean a place that is far away, in the middle of nowhere, and/or exotic.
Podunk is used in American English for a hypothetical small town regarded as typically dull or insignificant, a place that you have likely never heard of, though still in the United States. Another example is East Cupcake to refer to a generic small town in the Midwestern United States.
In New Zealand English, Woop Woops (or, alternatively, Wop-wops) is a (generally humorous) name for an out-of-the-way location, usually rural and sparsely populated. The similar Australian EnglishWoop Woop, (or, less frequently, Woop Woops) can refer to any remote location, or outback town or district. Another New Zealand English term with a similar use is Waikikamukau ("Why kick a moo-cow"), a generic name for a small rural town.
Mopery: used in informal legal discussions as a placeholder for some infraction, when the exact nature of the infraction is not important.
Blackacre and its neighbors Whiteacre, Greenacre, Brownacre, Greyacre, Pinkacre, etc. are used as placeholders for parcels of real property, usually on Law School examinations and the several State Bar Exams. They are sometimes located in Acre County in the fictional State of Franklin.
St. Elsewhere is often used as a placeholder name for any regional hospital or other care facility from which an admitted patient was referred. The medical slang is honored in the name of the 1980s television show of the same name.
GOMER (get out of my emergency room) is a name in medical slang for any patient who continually uses emergency room services for non-emergency conditions; its use is informal and pejorative. See Gomer for its possible origin.
Often used in example names and addresses to indicate to the serviceman where to put his own details.
In the US Army and Air Force, Private (or Airman) Tentpeg and Snuffy are commonly used in examples (to explain various procedures) or cautionary tales. In the Marine Corps, Lance Corporal Schmuckatelli serves the same purpose.
In the US Coast Guard, a generic Coast Guardsman is referred to as Joe Coastie (or Jane).
In the Coast Guard, Navy, and Marines, a hypothetical member who has his act together is A.J. Squared-Away.
In the Canadian Armed Forces, the generic name for a soldier is Private/Corporal/rank Bloggins
^Gail Collins (April 30, 2014). "It's Only a Million". New York Times. It will never occur to them that if voters had not given them that stint of public service, they would be processing divorce cases back home in East Cupcake.