DuckCorp Dico

Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   ENQ
      1. <character> /enkw/ or /enk/ ENQuire.  The mnemonic for
      ASCII character 5.
      2. <chat> An on-line convention for querying someone's
      availability.  After opening a chat connection to someone
      apparently in heavy hack mode, one might type "SYN SYN ENQ?"
      (the SYNs representing notional synchronisation bytes), and
      expect a return of ACK or NAK depending on whether or not
      the person felt interruptible.
      Compare ping, finger.
      [Jargon File]
      (1998-01-18)