If you have a mobile phone and travel to other areas or countries, you can still use it to make and receive a call. Your phone number does not change. This is called roaming in the wireless telecommunications.
In the cloud environment, your virtual machine can “travel” around as well, maybe from one datacenter to another, from your enterprise to one of your service providers or the other way around, or from one service provider to another.
It’s relatively easy for a virtual machine