Definition · applies to numbers

Elementary

A cardinal number is a number that tells how many.

Graduate (set theory)

The cardinal number of a set is its cardinality. Two sets have the same cardinal number if there is a bijection between them.

Properties

  • The cardinal numbers include the natural numbers and infinite cardinals, such as $\aleph_0$, the cardinality of $\mathbb{N}$.

All definitions · All distinctions · All examples