Wiktionary
uncountable set
n. (context mathematics English) A set, containing infinite number of elements, whose elements can not be mapped one-to-one to the natural numbers. A set with a cardinality greater than that of the set of natural numbers.
Wikipedia
Uncountable set
In mathematics, an uncountable set (or uncountably infinite set) is an infinite set that contains too many elements to be countable. The uncountability of a set is closely related to its cardinal number: a set is uncountable if its cardinal number is larger than that of the set of all natural numbers.