Noun
Zermelo set theory
(set theory) An early and influential axiomatisation of set theory.
Indeed, Zermelo set theory already can interpret second-order arithmetic and much of type theory in finite types, which in turn are sufficient to formalize the bulk of mathematics. Source: Internet
The system of PM is roughly comparable in strength with Zermelo set theory (or more precisely a version of it where the axiom of separation has all quantifiers bounded). Source: Internet