Unique
The property of being the only possible solution (perhaps modulo a constant, class of transformation, etc.).
See also
Essentially Unique, Existence, Unique Factorization, Uniqueness TheoremExplore with Wolfram|Alpha
WolframAlpha
Cite this as:
Weisstein, Eric W. "Unique." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Unique.html