2. (Especially Unix) Any terminal at all; sometimes used to refer to the particular terminal controlling a given job (it is also the name of a Unix command which outputs the name of the current controlling terminal).
3. (Unix) Any serial port, whether or not the device connected to it is a terminal; so called because under Unix such devices have names of the form tty*. Ambiguity between senses 2 and 3 is common but seldom bothersome.
4. A TDD.