In mathematics, a countable set is a set with the same cardinality (number of elements) as some subset of the set of natural numbers. A set that is not countable is called uncountable. The term was originated by Georg Cantor. The elements of a countable set can be counted one at a time and although the counting may never finish, every element of the set will eventually be associated with a natural number.
Some authors use countable set to mean a set with the same cardinality as the set of natural numbers.[1]
The difference between the two senses of countable set is in how they handle finite sets. Under the first definition finite sets are considered to be countable, while under the second definition they are not. To resolve this ambiguity, the term at most countable is sometimes used for the first definition, and countably infinite for the second.
The term denumerable can also be used to me