Admissible set

In mathematics, particularly in the context of set theory, an **admissible set** refers to a certain type of set that satisfies specific properties related to the theory of ordinals and higher-level set theory. In model theory and descriptive set theory, an admissible set is typically defined within the framework of **Zermelo-Fraenkel set theory (ZF)** augmented by the Axiom of Choice (though in some contexts, it is discussed without the Axiom of Choice).