I meant if you install it on your real machine and have to activate it once, can you still run it on VirtualBox? Because I assume you can only install Windows on one machine.
True. With a volume license, you can install Windows up to the maximum number of machines allowed by the license.
If it's an OEM license, it can only legally be used on the computer it came with. If it's never been activated before, then you should be able to activate it, and it will be activated as genuine copy of Windows. But just because it's activated does not make it legal. I guess in some European countires, you can do this legally, but not you can't elsewhere.