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Placeholder term used in computer science
metasyntactic variables in computer science and programming
A metasyntactic variable is a specific word or set of words identified as a placeholder in computer science and specifically computer programming. These words are commonly found in source code and are intended to be modified or substituted before real world usage. For example, foo and bar are used in over 330 Internet Engineering Task Force Requests for Comments, the documents which define foundational internet technologies like HTTP (web), TCP/IP, and email protocols. 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. Two of these words, plugh and xyzzy, are taken from the game Colossal Cave Adventure. A complete reference can be found in a MIT Press book titled The Hacker's Dictionary.

In Japanese, the words (ほげ) and (ふが) are commonly used, with other common words and variants being piyo (ぴよ), (ほげら), and (ほげほげ). The origin of as a metasyntactic variable is not known, but it is believed to date to the early 1980s.

In the Italian software programming culture, it is common to encounter names of Walt Disney characters being used as variables. These names often appear in pseudo code, are referenced in Software Engineering classes, and are commonly employed when explaining algorithms to colleagues. Among the most frequently used are "pippo" (Goofy), "pluto," and "paperino" (Donald Duck).

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.