A command line is a text-based interface used to interact with a computer's operating system. Instead of using a graphical user interface (GUI) with buttons and icons, users type commands to perform tasks like managing files, running programs, or configuring system settings. This method can be more efficient for experienced users. Command lines are commonly found in operating systems like Windows, macOS, and Linux. Each system has its own command line interpreter, such as Command Prompt for Windows or Terminal for macOS and Linux. Learning to use command lines can enhance productivity and provide greater control over the computer.