A terminal is a text input point in a computer that is also called the Command Line Interface (CLI).

IBM 3270, VT100 and many others are hardware terminals that are no longer produced as physical devices. To emulate these terminals, there are terminal emulators.

Emulation is the ability of a computer program to imitate another program or device.

A terminal emulator, also called tty, is a software program that emulates a video terminal in modern computers that use graphical user interfaces and provide interactive access to applications that run only in the command line environments. These applications may be running either on the same machine or on a different one via telnet, ssh, or dial-up.

Virtual Terminal Environment (VTE) is a terminal emulator which emulates a text terminal inside a graphical user interface (GUI) environment. Terminal is largely based on the VTE. VTE has widgets that implement a fully functional terminal emulator.

A shell is a program that provides an interface to invoke or “launch” commands or another program inside a terminal. It also allows you to view and browse the contents of directories. Popular shells include bash, zsh, fish.

An escape sequence is a series of characters used to change the meaning of data in a terminal. Escape sequences are used when a computer has only single channel to send information back and forth. Escape sequences are used to distinguish if data being sent is a command to be executed or information to be stored and displayed.

A prompt is also called a command prompt. It is a sequence of characters used in the command line environment to indicate the readiness of the shell to accept commands.

A prompt usually ends with the characters $, %, # or > and includes information about the path of the present working directory. On Unix based systems, it is common for the prompt to end in a $ or # character depending on the user role such as $ for user and # for superuser (also called root).

An input entered in the prompt to be executed is called a command. It is a combination of the program name along with any other additional parameters passed as flags to alter the execution of the program.