aleph (thing)

(Set Theory:)

Aleph (ℵ), unadorned with subscripts, is the common symbol for the cardinality of the continuum.

2^ℵ₀ = ℵ

With subscript 0, ℵ₀ (aleph-null) is the cardinality of the integers. With successive (ordinal) subscripts, ℵ_z is the z'th cardinal after ℵ₀. The Continuum Hypothesis (CH) is that ℵ = ℵ₁.