Source : Free On-Line Dictionary of Computing

control code
     
         A character which is input or output to cause some
        special action rather than to appear as part of the data.
     
        Most control characters are input by holding down (either of)
        the "Control" key(s) on the keyboard and simultaneously
        pressing another key which may be a letter or (depending on
        the keyboard and {operating system}) certain punctuation
        characters.  Some control codes usually have their own special
        keys: {escape}, {tab}, {delete}, {backspace}, {return} and can
        thus be entered with a single keypress.
     
        Different {operating system}s and programs have different
        conventions for what effect typing certain control codes will
        have, such as interrupting the current process or suspending
        output.
     
        Control codes may be output for their effect on the output
        device, e.g. moving the cursor or print head to the start of a
        new line.
     
        See {control-O}, {control-Q}, {control-S}.
     
        (1995-03-23)