A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video terminal within some other display architecture.
From : en.wikipedia.org/wiki/Terminal_emulator
A program that allows your computer to pretend that it is an unintelligent box capable of sending and receiving textual information - Telnet is accessed by a terminal emulator
From : www.archivemag.co.uk/gloss/T.html