Topos

In mathematics, a topos (US: /ˈtɒpɒs/, UK: /ˈtoʊpoʊs, ˈtoʊpɒs/; plural topoi /ˈtɒpɔɪ/ or /ˈtoʊpɔɪ/, or toposes) is a category that behaves like the category of sheaves of sets on a topological space (or more generally: on a site). Topoi behave much like the category of sets and possess a notion of localization; they are a direct generalization of point-set topology. The Grothendieck topoi find applications in algebraic geometry; the more general elementary topoi are used in logic.

The mathematical field that studies topoi is called topos theory.