Congratulations! you have installed linux as your first vm. the gui is nice and you'll get the feel for it quickly (unless you already have you will become a fan of vms once you break something. remember from earlier right after installing make a copy or more of the file. that's your hard drive!

The answer is VHD (Virtual Hard Disk) file. VHD (Virtual Hard Disk) is a format which represents a virtual hard disk drive similar to the (HDD). It may contain what is found usually on a physical HDD, such as disk partitions and a file system. It is typically used as the hard disk of a virtual machine.