Text user interface or textual user interface (TUI), or terminal user interface,^{[clarification needed]} is a retronym that was coined sometime after the invention of graphical user interfaces, to distinguish them from text-based user interfaces. The concept of TUI refers primarily to the way of output and does not coincide with command-line interfaces which is a certain user input mode. An advanced TUI may, like GUIs, use the entire screen area and does not necessarily provide line-by-line output, although TUIs only use text, symbols and colors available on a given text terminal or text mode display.

American National Standards Institute (ANSI) standard ANSI X3.64 defines a standard set of escape sequences that can be used to drive terminals to create TUIs (see ANSI escape code). However, not all terminals follow this standard, and many non-compatible but functionally equivalent sequences exist.

On IBM Personal Computers and compatibles, the Basic Input Output System (BIOS) and DOS system calls provide a way to write text on the screen, and the ANSI.SYS driver could process standard ANSI escape sequences. However, programmers soon learned that writing data directly to the screen buffer was far faster and simpler to program, and less error-prone. This change in programming methods resulted in many DOS TUI programs.

The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the machine which aids the operator in making operational decisions. Examples of this broad concept of user interfaces include the interactive aspects of computer operating systems, hand tools, heavy machinery operator controls, and process controls. The design considerations applicable when creating user interfaces are related to or involve such disciplines as ergonomics and psychology.

A user interface is the system by which people (users) interact with a machine. The user interface includes hardware (physical) and software (logical) components. User interfaces exist for various systems, and provide a means of:

Generally, the goal of human-machine interaction engineering is to produce a user interface which makes it easy, efficient, and enjoyable to operate a machine in the way which produces the desired result. This generally means that the operator needs to provide minimal input to achieve the desired output, and also that the machine minimizes undesired outputs to the human.