Datacenter is the ultimate package – you must license every physical processor in a server, but then you are allowed to run the software in the physical environment and an unlimited number of virtual environments on the licensed server. You are also granted an unlimited number of simultaneous running instances on a licensed server. This makes licensing much easier to deal with as you don’t have to track instances across your servers and worry about being under-licensed.
You are also permitted to run any software or application you have licensed in the physical environment.
While this sounds like a dream come true, you still need to do your due diligence to ensure you’re getting the right package, licensing, etc.