[1] : Jargon File (4.3.1, 29 Jun 2001)

control-o vi. "stop talking." from the character used on some operating
   systems to abort output but allow the program to keep on running.
   generally means that you are not interested in hearing anything more
   from that person, at least on that topic; a standard response to someone
   who is flaming. considered silly. compare control-s.


see also:
control-s 

[2] : The Free On-line Dictionary of Computing (27 SEP 03)

control-o
     
         ascii character 15 si.
     
        the character used on some operating systems to abort output
        but allow the program to keep on running.  the name "si" comes
        from its use on some terminals to "shift in" an alternative
        character set.  "so" is control-n.
     
        compare control-s.
     
        jargon file
     
        1995-03-16
     
     
see also:
ascii operating system control-n control-s jargon file 

Control-O >> C Words
Control-O, definition of term: Control-O
control-o_pag1.html