
When you click on the "Close" button of your virtual machine window (at the top right of the window, just like you would close any other window on your system), VirtualBox asks you whether you want to "save" or "power off" the VM. (As a shortcut, you can also press the Host key together with "Q".)
The difference between these three options is crucial. They mean:
Save the machine state: With this option, VirtualBox "freezes" the virtual...