On Unix or Unix-like systems, it may be any of a variety of programs such as bash, ksh, etc. This program accepts commands typed from a prompt and executes them, usually in real time, displaying the results to what is referred to as standard output, usually a monitor or screen.
This program acts as a command processor on Unix or Unix-like operating systems. It takes commands typed by users from the prompt and runs them immediately, showing the results on the screen.