Source : Free On-Line Dictionary of Computing

bus error
     
         A fatal failure in the execution of a {machine
        language} instruction resulting from the {processor} detecting
        an anomalous condition on its {bus}.  Such conditions include
        invalid address alignment (accessing a multi-byte number at an
        odd address), accessing a {physical address} that does not
        correspond to any device, or some other device-specific
        hardware error.  A bus error triggers a processor-level
        {exception} which {Unix} translates into a "SIGBUS" {signal}
        which, if not caught, will terminate the current process.
     
        (2000-04-04)