The keyboard shortcut "Alt + F4" is commonly used in the Windows operating system to close the currently active window or application. When this combination is pressed, it sends a command to terminate the program, prompting the user to save any unsaved work before closing. In many cases, "Alt + F4" can also bring up a shutdown dialog if used on the desktop, allowing users to shut down or restart their computer. This shortcut is a quick way to manage open applications without needing to navigate through menus or use a mouse.