An infinite set, such as the real numbers, which is not countably infinite.
Uncountably Infinite
See also
Aleph-0, Aleph-1, Countable Set, Countably Infinite, Finite, Infinite, InfinityExplore with Wolfram|Alpha
References
Croft, H. T.; Falconer, K. J.; and Guy, R. K. Unsolved Problems in Geometry. New York: Springer-Verlag, p. 2, 1991.Referenced on Wolfram|Alpha
Uncountably InfiniteCite this as:
Weisstein, Eric W. "Uncountably Infinite." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/UncountablyInfinite.html