Sentence:  The main point of <WSD>scheme theory</WSD> is to consider C as a covariant functor R\mapsto C(R) from the category \textit{B-ALG} (also written as \textit{ALG}_{/ \mathfrak{B) of \mathfrak{B}-algebras into the category \textit{SETS} of sets. 
Meaning of the word marked with <WSD> tags:  The branch of mathematics that concerns schemes (algebraic varieties equipped with the Zariski topology).