What does aleph-null represent in set theory?

In set theory, aleph-null (${\aleph }_0$) represents the smallest transfinite cardinal number. It denotes the cardinality—or the number of elements—of the infinite set of natural numbers {1, 2, 3, …}.12

Any set that can be placed into a one-to-one correspondence with the natural numbers is considered to have a cardinality of ${\aleph }_0$ and is described as denumerable or countably infinite. For instance, the set of even numbers and the set of all integers are both countably infinite, as they can be paired with the natural numbers.231

Introduced by the mathematician Georg Cantor, ${\aleph }_0$ serves as the starting point for an infinite hierarchy of cardinal numbers. While ${\aleph }_0$ is infinite, it is smaller than other transfinite numbers, such as the cardinality of the real numbers, which is known as the continuum (c).23