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.
On Unix or Unix-like systems, this program can be any of several programs such as bash or ksh. It takes commands entered at a prompt and runs them immediately, showing the results on the screen, which is referred to as standard output.