It looks like you are referring to Command Line Interface or shortened CLI.It is, basically, a tool that is used for input and output.
It contains command lines which are put on the screen by a user.
It is only put with a keyboard and is an complete different thing than GUI, which is commands are put in with the mouse, so you have a difference in with what device you put it in.
It is much more powerful than GUI and reliable and is usually self-documenting.
MS-DOS is the most common example of CLI.
I hope I helped a little, let me know in a reply.
It's essentially the command line interface used to manage Linux. Windows and some desktop Linux OS uses GUI (graphic user interface), but when managing Linux servers you use CLI.
It's basically your method of interacting with the server, to install/uninstall software, security updates, manage the functionality of the server etc.
You could manage PHP with it, but not the easiest. A control panel (like cpanel) would make your life easier for this