Short for ''pseudo teletype'', but more commonly referred to as a pseudo terminal.

A pseudo terminal is a pair of character devices, a master device, and a slave device. These allow communication between an application process and a server process. When sending data to pty devices (such as windows), a pty device must exist for every window that is open at any given time.

Also see [expect], a Tcl extension which deals nicely with ptys
on UNIX.  Alas, on Windows things are a bit problematic.  And
on other Operating Systems, things can be even worse...