The Free On-line Dictionary of Computing (19 January 2023):

control-Q
DC1
XON

    (XON, DC1, Device Control 1, ASCII code
   17).  A control character, used in software handshaking to
   resume output after a previous control-S.

   [Jargon File]

   (2020-03-01)


The Jargon File (version 4.4.7, 29 Dec 2003):

control-Q
 vi.

    “Resume.” From the ASCII DC1 or XON character (the pronunciation /X-on/
    is therefore also used), used to undo a previous control-S.