undefined.
Lacking a definition or value.
Meaning & usage
Lacking a definition or value.
That does not have a logically sound meaning within a specific formal system and is thus not assigned an interpretation.
The result of division by zero is undefined.
Within the set of real numbers, the square root of a negative number is undefined.
That behaves unreliably due to dependence on an uninitialized value or inconsistently ported code.
In C, relying on a variable's value right after a malloc call is undefined behvaior.
Where this word comes from
Etymology tree Proto-Indo-European *né Proto-Indo-European *n̥- Proto-Germanic *un- Proto-West Germanic *un- Old English un- Middle English un- English un- English defined English undefined From un- + defined.
An undefined value.
Where this word comes from
Etymology tree Proto-Indo-European *né Proto-Indo-European *n̥- Proto-Germanic *un- Proto-West Germanic *un- Old English un- Middle English un- English un- English defined English undefined From un- + defined.
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Definitions, grammatical labels, IPA, etymology and examples: Wiktionary contributors, extracted by Kaikki / Wiktextract. Adapted under CC BY-SA 4.0. Selected fields and authored examples are shown; third-party quotations and audio are omitted. See contributor history.
Last enriched 2026-09-10. Definitions are in English. Romanizations are shown when supplied by the source; syllable estimates are omitted for unsupported scripts.