Sentence:  One defines in like manner "right" "K"-<WSD>modules</WSD> and "two-sided" "K"-<WSD>modules</WSD>. If "K" is commutative, then every left "K"-<WSD>module</WSD> is automatically equipped with the structure of right and a two-sided "K"-<WSD>module</WSD>. 
Meaning of the word marked with <WSD> tags:  An abelian group equipped with the operation of multiplication by an element of a ring (or another of certain algebraic objects), representing a generalisation of the concept of "vector space" with "scalar multiplication".