A placeholder name is any one of several types of term used instead of forgotten, unknown, or irrelevant words. Such words perform various functions in several categories.
For example, in social situations, words like buddy, dude, fellow (or fella), mac, and pal are colloquial stand-ins when addressing a person whose name is not known to the speaker. More formal variations are sir (for men), ma’am (for women), and miss (for younger women). Terms of endearment include baby, honey, dear, darling, and the like. Hon, short for honey, is also used in the American South as a casual term equivalent to buddy.
Given names also fill this need. Jack, a nickname for John, for much of modern English history the most common male first name, was also employed in Jack Tar, identifying the common sailor. (The invented surname came about due to the ubiquity of the scent of tar among rank-and-file seamen.) John also became a slang euphemism for a prostitute’s client, because most men in this position wish to remain anonymous.
Various hypothetical names serve in different social contexts: John Q. Public, originally used as a sample name on government forms, represents the typical American citizen; Joe Blow and Joe Sixpack are more colloquial versions implying an Everyman (that word itself is a placeholder name) with rudimentary sensibilities.
George Spelvin is a name used by actors who for some reason do not want to reveal their names, or to disguise on a list of characters and the actors who portray them that a character does not appear in a play or is played by a person appearing in another role. The directorial equivalent is Alan Smithee, a name occasionally employed by a director who disowns a film because of studio interference in its production.
Meanwhile, John Doe, Jane Roe, and the like are employed to stand in for plaintiffs in a legal case when the identity of the party is irrelevant or should be protected. Law enforcement agencies often use these types of terms as well, as when the perpetrator or the victim of a crime has not yet been identified.
The geographical placeholder name Anytown, like John Q. Public, comes from sample versions of forms. Derogatory equivalents include Hicksville and Podunk for backward rural locations, and the name of the actual Illinois municipality of Peoria was also long frequently employed (and occasionally still is) to stand for communities populated by unsophisticated people who may not appreciate cultural offerings (“Will it play in Peoria?”); the real places Outer Mongolia or Timbuktu have been used to represent the ultimate in remote locales.
The many number placeholders include “a ton,” buckets, heaps, oodles, and the like, or to represent smaller amounts, “a bit” or “a couple of” (or the slang variants “a couple-few” or “a couple-three”). Other words referring to large amounts include umpty and intensifiers of -illion such as zillion or kajillion.