Aleph (ℵ), unadorned with subscripts, is the common symbol for the cardinality of the continuum.
2ℵ0 = ℵ
With subscript 0, ℵ0 (aleph-null) is the cardinality of the integers. With successive (ordinal) subscripts, ℵz is the z'th cardinal after ℵ0. The Continuum Hypothesis (CH) is that ℵ = ℵ1.