Source : Free On-Line Dictionary of Computing

Non-Maskable Interrupt
     
        (NMI) An IRQ 7 on the {PDP-11} or {680x0} or the NMI line on
        an 80x86.  In contrast with a {priority interrupt} (which
        might be ignored, although that is unlikely), an NMI is
        *never* ignored.
     
        (1994-12-13)