The Collaborative International Dictionary of English v.0.48:

offset printing \off"set print"ing\, n. (Printing)
   A printing technique in which a lithographic image on an
   inked metal or stone plate is transferred first to a rubber
   sheet (usually on a cylinder) before transfer to the paper.
   Called also offset lithography.
   [PJC]

WordNet (r) 3.0 (2006):

offset printing
    n 1: a plate makes an inked impression on a rubber-blanketed
         cylinder, which in turn transfers it to the paper [syn:
         offset, offset printing]