Undefine

Undefine is a technical verb used to describe removing or cancelling an existing definition of a name, symbol, or bound entity. It is applied across programming languages, build systems, and configuration contexts to revert a previous binding so that the name either has no definition or must be redefined.

In C and C++, the preprocessor directive #undef NAME removes a macro definition that was defined earlier with #define. After #undef NAME, occurrences of NAME are not replaced by the macro body and may cause errors if used again unless redefined.

In GNU Make, the undefine directive can delete the contents of a variable, removing its value and any references. This is useful for rebuilding or overriding variable definitions in included makefiles or during conditional builds.

In shell scripting, the concept is realized by unsetting a variable or function, often via the unset command, which can be considered a related operation to undefine in other systems. It removes the binding of a name in the current environment and may affect subsequent commands that rely on that binding.

In data modeling and configuration, undefine may refer to removing a defined field, attribute, or constraint, effectively reverting the item to an undefined state. Specific terminology and mechanisms vary by platform, language, or tool.

Notes: The term is not universally standardized; some contexts prefer “remove the definition” or “delete binding” rather than “undefine.” Its exact effect depends on the system: it often makes a symbol unbound and may trigger errors if referenced without a new definition.

See also: define, undefined behavior, unbinding, unset.