I'm taking a look at Introduction to Algebraic Geometry and Algebraic Groups by Michael Demazure and Peter Gabriel, and I'm confused about some terminology. Early in the book it says "A $\mathbb{Z}$-functor is a functor from the category of models $M$ into the category of sets $E$. The category of $\mathbb{Z}$-functors is denoted $ME$."
What is the category of models? This book uses some rather nonstandard terminology, for example when they say geometric space, they mean a locally ringed space, and spectral space seems to refer to what everyone else calls a scheme.