In Sweden, when we don't use a vehicle, we tell our local DMV that it's not going to be on the road. Then, they sign it as such and we can pay less or no insurance (although we're extremely limited in terms of the permitted usage).
I want to tell that to someone about a vehicle and initially I said that it might be unregistered but that's not correct terminology. The vehicle is registered, it has plates and an owner.
What's the correct term for it in English? As it's a legal term, I wouldn't be surprised if it's different on the different sides of the oceans.