ZF set theory

ZF Set-Theory is a short-form for: "Zermelo–Fraenkel set theory." The page you are reading is about set-theory. This system was named after mathematicians Ernst Zermelo and Abraham Fraenkel. ZF Set-Theory was created via the means of an axiomatic systems that devised was in early twentieth-century to formulate a theory of sets that cleanly contained paradoxes such as Russell's paradox.

(https://mathworld.wolfram.com/Zermelo-FraenkelAxioms.html)