What does UUID mean? Is it used to identify and reference virtual
Yes, you are right. A universal unique identifier (UUID) is a 128-bit number used to uniquely identify each virtual machines. It is stored in the SMBIOS system information descriptor. It can be accessed by standard SMBIOS scanning software and used for system management in the same way you use the UUID of a physical computer.
The UUID is generated when you power on or reset the virtual machine. As long as you do not move or copy the virtual machine to another location, the UUID remains constant.
Fore more read the documentation.
You can use:
VBoxManage list vms
to list all currently registered VMs with their settings, names and UUIDs.
Once you know the UUID you can also start a vm by:
VBoxManage startvm <UUID-of-vm>
which is essentially same as:
VBoxManage startvm "Name-of-vm"