The Collaborative International Dictionary of English v.0.48:

PBS \PBS\ n.
   1. (Biochem.) [Initialism] Phosphate-buffered saline, a
      saline solution containing a phosphate buffer.

   Syn: phosphate-buffered saline.
        [PJC]

   2. [Initialism] Public Broadcasting System; a system of
      non-profit radio and television broadcasting stations.
      [PJC]

WordNet (r) 3.0 (2006):

PBS
    n 1: a solution containing a phosphate buffer [syn: phosphate
         buffer solution, PBS]