With the seamless windows feature of Oracle VM VirtualBox, you can have the windows that are displayed within a virtual machine appear side by side next to the windows of your host. This feature is supported for the following guest operating systems, provided that the Guest Additions are installed:
Windows guests.
Supported Linux or Oracle Solaris guests running the X Window System.
After seamless windows are enabled, Oracle VM VirtualBox suppresses the display of the desktop background of your guest, allowing you to run the windows of your guest operating system seamlessly next to the windows of your host.
To enable seamless mode, after starting the virtual machine, press the Host key + L. The Host key is normally the right control key. This will enlarge the size of the VM's display to the size of your host screen and mask out the guest operating system's background. To disable seamless windows and go back to the normal VM display, press the Host key + L again.