Sentence:  "verso" left-hand page of a book usually identified with even <WSD>folio</WSD> numbers. ... "recto" right-hand page of a book usually identified with odd <WSD>folio</WSD> numbers. 
Meaning of the word marked with <WSD> tags:  A page number. The even folios are on the left-hand pages and the odd folios on the right-hand pages.