Metasyntactic variable

Strictly, a variable used in metasyntax, but often used for any name used in examples and understood to stand for whatever thing is under discussion, or any random member of a class of things under discussion. The word foo is the canonical example. To avoid confusion, hackers never (well, hardly ever) use "foo" or other words like it as permanent names for anything. In filenames, a common convention is that any filename beginning with a metasyntactic-variable name is a scratch file that may be deleted at any time. "foo" and "bar" are universal (and baz nearly so). The compounds foobar and "foobaz" also enjoy very wide currency. Some jargon terms are also used as metasyntactic names; barf and mumble, for example. See also Commonwealth Hackish for discussion of numerous metasyntactic variables found in Great Britain and the Commonwealth.

Free Online Dictionary of Computing