The Collaborative International Dictionary of English v.0.48:

assembly line \assembly line\ n.
   A line of machinery, tools, and workers on which objects to
   be manufactured are moved from one post to the next, where
   different workers perform different steps in the
   manufacturing process; called also production line. The
   objects to be manufactured usually move on a form of conveyor
   belt, which does not necessarily move only in a straight
   line, but may continue around the factory area for some
   distance.
   [PJC]

WordNet (r) 3.0 (2006):

assembly line
    n 1: mechanical system in a factory whereby an article is
         conveyed through sites at which successive operations are
         performed on it [syn: production line, assembly line,
         line]