WordNet (r) 3.0 (2006):

control character
    n 1: ASCII characters to indicate carriage return or tab or
         backspace; typed by depressing a key and the control key at
         the same time [syn: control character, ASCII control
         character]

The Free On-line Dictionary of Computing (30 December 2018):

control character

    Any of a number of special characters that exist in
   most coded character sets and that are input or output to cause
   some special action rather than as part of the normal textual
   data.

   Control characters are input by holding down a control key on
   the keyboard and simultaneously pressing a letter key or
   (depending on the keyboard and operating system) certain
   punctuation characters.  Some control codes have their own special
   keys: escape, tab, delete, backspace, return, allowing
   them to be entered with a single key press.

   Control characters 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 (carriage return, Control-M), advancing
   down to the next line (line feed, Control-J) or ringing the
   bell (Control-G).

   Different operating systems and application programs have
   different conventions for what effect typing certain control
   characters will have, such as interrupting the current process
   (Unix Control-C) or suspending or resuming output
   (Control-S, Control-Q).

   See ASCII character table.

   (2015-03-07)