Source : Free On-Line Dictionary of Computing

embedded system
     
         Hardware and software which forms a component of
        some larger system and which is expected to function without
        human intervention.
     
        A typical embedded system consists of a single-board
        {microcomputer} with software in {ROM}, which starts running
        some special purpose {application program} as soon as it is
        turned on and will not stop until it is turned off (if ever).
     
        An embedded system may include some kind of {operating system}
        but often it will be simple enough to be written as a single
        program.  It will not usually have any of the normal
        {peripheral}s such as a keyboard, monitor, serial connections,
        mass storage, etc. or any kind of user interface software
        unless these are required by the overall system of which it is
        a part.  Often it must provide {real-time} response.
     
        {Usenet} newsgroup: {news:comp.arch.embedded}.
     
        (1995-04-12)