Generally, it needs to fall into the category of "Uninhabitable Space". You could potentially call it a storage space, a workshop, or something else clever, but those terms may ultimately get shot down the AHJ (Authority Having Jurisdiction, such as a local building department) because if it looks and smells like it could be habitable space, they may be tempted to make you finish it anyways regardless of what you call it.
So in that case, the best recommendation I can give is to talk to the Authority Having Jurisdiction about the purpose of the room and how best to describe it in the plans. Since they will be approving the plans, they would be best able to help you come up with a term for the space that they would approve.