Source : Free On-Line Dictionary of Computing

approximation algorithm
     
         An {algorithm} for an {optimisation} problem that
        generates {feasible} but not necessarily {optimal} solutions.
     
        Unlike "{heuristic}", the term "approximation algorithm" often
        implies some proven worst or average case bound on
        performance.  The terms are often used interchangeably
        however.
     
        (1997-10-28)