Source : Free On-Line Dictionary of Computing

GPSS
     
        General Purpose Systems Simulator.  Geoffrey Gordon, 1960.
        Discrete simulations.  "The Application of GPSS V to Discrete
        System Simulation", G.  Gordon, P-H 1975.  Versions include
        GPSS II (1963), GPSS III (1965), GPS/360 (1967), and GPSS V
        (1970).