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