The command line is a text-based interface used to interact with a computer's operating system or command-line interface (CLI). It allows users to issue commands and perform various tasks by typing in text commands, rather than using a graphical user interface (GUI).

When using the command line, users can navigate through files and directories, create and delete files and directories, run programs, and perform various system maintenance tasks. Commands are typically entered into a command prompt, which is a text-based interface that displays information about the current directory and other system information.

The command line can be found on many operating systems, including Windows, macOS, and Linux. It is often used by developers, system administrators, and power users who need to perform complex tasks quickly and efficiently. While it can be intimidating at first, learning how to use the command line can be a valuable skill that can greatly enhance one's productivity and efficiency when working with a computer.

Below is an example of the "Terminal" application which is used on machines that run MacOS.