A symbol representing infinite cardinal numbers and transfinite sets in set theory and mathematical logic.
Examples
Denoting the cardinality of natural numbers (aleph-null)
\aleph_0 = |\mathbb{N}|
Comparing infinite cardinal numbers
2^{\aleph_0} = \aleph_1 \text{ (Continuum Hypothesis)}
Set theory cardinality comparison
|\mathbb{R}| = \aleph_1 > \aleph_0 = |\mathbb{N}|