is a symbol that represents a quantity with no defined value.


Undefined
is a symbol that represents a quantity with no defined value.
Details

- Computations like ConditionalExpression[expr,False] generate Undefined.
- If Undefined appears in an argument of a mathematical function, equation, inequality, or Boolean operator the result will be Undefined.
Examples
Basic Examples (2)
ConditionalExpression with False condition evaluates to Undefined:
The number of solutions depends on the value of x:
For x=1 only the first solution is defined:
Mathematical expressions containing Undefined evaluate to Undefined:
See Also
Related Guides
History
Text
Wolfram Research (2010), Undefined, Wolfram Language function, https://reference.wolfram.com/language/ref/Undefined.html.
CMS
Wolfram Language. 2010. "Undefined." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Undefined.html.
APA
Wolfram Language. (2010). Undefined. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Undefined.html
BibTeX
@misc{reference.wolfram_2025_undefined, author="Wolfram Research", title="{Undefined}", year="2010", howpublished="\url{https://reference.wolfram.com/language/ref/Undefined.html}", note=[Accessed: 13-August-2025]}
BibLaTeX
@online{reference.wolfram_2025_undefined, organization={Wolfram Research}, title={Undefined}, year={2010}, url={https://reference.wolfram.com/language/ref/Undefined.html}, note=[Accessed: 13-August-2025]}