If you have your login window set to show the Name and Password fields (as opposed to the "List of users" or auto-login), you will see a window like the one shown above when your Mac first boots, when you logout, or when you change to the login window if you have Fast User Switching enabled.
OS X has supported several "special" login names for a long time. Each is entered into the "Name" field with no password. They are:
>restart
>shutdown
>sleep
>console
You can probably guess what the first three do. The fourth one ">console" will drop you to a shell login prompt, where you can login with your username and password if you want quick access to a shell instead of the full user interface. The restart/shutdown/sl
