A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video terminal within some other display architecture.
Though typically synonymous with a command line shell or text terminal, the term terminal covers all remote terminals, including graphical interfaces. A terminal emulator inside a graphical user interface is often called a terminal window.

A terminal window allows the user access to text terminal and all its applications such as command-line interfaces (CLI) and text user interface applications. These may be running either on the same machine or on a different one via telnet, ssh, or dial-up. On Unix-like operating systems it is common to have one or more terminal windows connected to the local machine.

Terminals usually support a set of escape sequences for controlling color, cursor position, etc.

Example programs providing the remote-access form of terminal emulation under Microsoft Windows include the built-in programs HyperTerminal and Microsoft's telnet client, as well as 3rd party programs like PuTTY, AlphaCom, SSH, Tera Term,SwitchTermJ and SecureCRT. A so-called "DOS box" or "Command prompt" is the Windows equivalent of a locally-connected terminal window (in fact, it is a Win32 console). MS-DOS examples include ProComm, Qmodem, Telemate and Telix.

The ubiquitous Unix terminal window is used for both local and remote access; where the connection goes is not the business of the terminal emulator itself, it just communicates through a pseudo terminal interface. Apple Computer ships Terminal with Mac OS X as its default terminal emulator. Many different terminal emulators are available for the X Window System, like aterm, dtterm, Eterm, GNOME Terminal, Konsole, rxvt, wterm,SwitchTerm and xterm.

Early adopters of computer technology, such as banks, insurance companies, and governments, still make frequent use of terminal emulators. They typically have decades old applications running on mainframe computers. The old “dumb” video terminals used to access the mainframe are long since obsolete; however, applications on the mainframe are still in use. Quite often, terminal emulators are the only way a user can access applications running on these older machines.