Source : Free On-Line Dictionary of Computing

pseudo-tty
     
        {Berkeley} {Unix} networking device which appears to an
        {application program} as an ordinary terminal but which is in
        fact connected via the network to a process running on a
        different {host} or a windowing system.  Pseudo-ttys have a
        slave half and a control half.  The slave tty (/dev/ttyp*) is
        the device that user programs use and the control tty
        (/dev/ptyp*) is used by {daemon}s to talk to the net.
     
        (1994-11-08)