May 23, 2026 · The meaning of UNDEFINED is not defined. How to use undefined in a sentence.

UNDEFINED meaning: 1. not clearly described, stated, or known: 2. not having been given a definition (= a statement…. Learn more.

not given meaning or significance, as by a definition; not defined or explained an undefined term

Sep 7, 2025 · The meaning of undefined with an overview, related terms, and examples from programming. Understand how undefined variables can lead to common error messages.

Look up undefined in Wiktionary, the free dictionary.

If it is undefined, it will not be equal to a string that contains the characters "undefined", as the string is not undefined. You can check the type of the variable:

1. not defined or explained. 2. indefinite in form or extent: an undefined feeling of sadness.