Think about the concept of virtual machines like VirtualBox or KVM for a bit. What do they do? They run virtual machines on physical hardware. Said hardware can be either a big tower PC or a small laptop, yet the exact same virtual machines can run on either hardware.
A virtual machine is software and software can be copied. Therefore virtual machines can be easily backed up and reverted to a previous state. Much the same way, virtual machines can easily be cloned or migrated to different hardware.
A virtual data center like Wakame-vdc extends this from a single machine to an entire data center. Wakame-vdc consists of several components that communicate through the network. You can install all these components together on a single laptop, or you can run them all on separate servers in a physical data center. On top of either, you are able to run a virtual data center.