1. in a manner that can be counted or enumerated; in a way that is finite or can be put into one-to-one correspondence with the natural numbers
Usage: primarily used in mathematics and logic; technical term

Examples

• The set of integers is countably infinite.
• In mathematics, we say a set is countably infinite if its elements can be listed in a sequence.
• The rational numbers are countably infinite, unlike the real numbers.
• A countably additive measure assigns values to countably many disjoint sets.
• The union of countably many finite sets is countable.