Ill-Defined
The term "ill-defined" is also used informally to mean ambiguous.
See also
Ambiguous, Ill-Posed, Well-DefinedExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Ill-Defined." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Ill-Defined.html