What Does Virtual Disk Image Mean?
A virtual disk image (VDI) is the image of a virtual hard disk or the logical disk associated with a virtual machine.
It is used in virtualization environments to create a replica of the disk space/drive assigned to one or more virtual machines.
Techopedia Explains Virtual Disk Image
VDI is primarily a method to create a copy/image/replica of a virtual machine’s hard disk to be later used for disk backup, restoration or copying to a new virtual machine. The VDI captures and stores all information on the primary disk, typically excluding the operating system files and the virtual machine itself.
In addition to being a disk image of a virtual hard disk, a virtual disk image can also refer to the disk image of a CD, DVD or any other optical disk.