A cardinal number is a number that expresses quantity. It tells us "how many" of something there are. For example, the numbers 1, 2, 3, and so on are cardinal numbers because they indicate specific counts of objects. Cardinal numbers can be finite (like 0, 1, 2, 3) or infinite (like the concept of infinity).
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In the presence of choice, a cardinal number may be represented by the least ordinal in its bijection class.