Idea
A geometric embedding in a Presheaf category. I.e it is a fully faithful functor that has an exact left adjoint.
Definition
A Grothendieck topos is just a category of sheaves on some site.
A geometric embedding in a Presheaf category. I.e it is a fully faithful functor that has an exact left adjoint.
A Grothendieck topos is just a category of sheaves on some site.