Shell - technical definition

The outer layer of a program that provides the user interface, or way of commanding the computer. The term originally referred to the software that processed the commands typed into the Unix operating system (see command line). For example, the Bourne shell was the original command line processor, and C shell and Korn shell were developed later. In DOS, the default shell was COMMAND.COM (see DOS Shell).

Later, the term was applied to graphical user interfaces (GUIs). For example, the default shell in Windows is Explorer, which provides the Start menu, taskbar and desktop. Alternative shells for Windows are also available. See Explorer, PowerShell, Bourne shell, C shell and Korn shell.