Metasyntactic variable

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A metasyntactic variable is either a placeholder name (a kind of alias term, commonly used to denote the subject matter under discussion), or a random member of a class of things under discussion. The term originates from computer programming.

The use of a metasyntactic variable is helpful in freeing a programmer from creating a logically named variable, although the invented term may also become sufficiently popular and enter the language as a neologism. The word foo is the canonical example.

The phenomenon is similar to the use in algebra of x, y and z for unknown variables, and a, b and c for unknown constants. "Widgets" are also used in business to indicate an as-yet-unspecified product and are frequently sold by the Acme company.

Metasyntactic variables are so called because:

1. They are variables in the metalanguage used to talk about programs, etc.
2. They are variables whose values are often variables (as in usages like "the value of f(foo, bar) is the sum of foo and bar").

Examples

Nonsense words

Foo, Bar, Baz, and Boo

Foo is the Canonical Metasyntactic Variable, commonly used to represent an as-yet-unspecified term, value, process, function, destination or event but seldom a person (see Ned Baker, below). It is sometimes combined with bar to make foobar. This suggests that foo may have originated with the World War II slang term fubar, as an acronym for fucked/fouled/"fixed" up beyond all recognition/repair, although the Jargon File makes a reasonably good case [1] that foo predates fubar.

See also

• Placeholder name (Kadigan)
• Free variables and bound variables
• Hello World
• Lorem Ipsum