from
The Free On-line Dictionary of Computing (8 July 2008)
control code
<character> 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 systems} 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)