ℵ₁, pronounced "aleph one," is a symbol used in set theory to represent the cardinality of certain infinite sets. Specifically, it denotes the smallest uncountable cardinal number, which is larger than the cardinality of the set of natural numbers, denoted by ℵ₀ (aleph null). In the context of the continuum hypothesis, ℵ₁ is often associated with the cardinality of the set of real numbers. This hypothesis posits that there are no sets whose cardinality is strictly between that of the integers and the real numbers, suggesting that ℵ₁ is equal to the cardinality of the continuum.