Source : Free On-Line Dictionary of Computing

ACIS
     
         Andy, Charles, Ian's System.
     
        A {geometric engine} that most {CAD} packages now use.  ACIS
        uses a sophisticated {object-oriented} approach for modelling,
        the data is stored in {boundary representation}.  Acis is
        owned by {Spatial Technologies}.
     
        [How does this differ from "solid modelling"?].
     
        (1996-03-21)