It's an ambiguous term. It could mean the item was a display item that was used and handled by every moron who came into a store, but it could also mean it was on display behind glass or in a supervised environment. It could also mean that it was literally opened for a customer to view the contents and never used, but this isn't the norm. It could be a return that is in perfect working order or one that was heavily used for a short time and returned.
Hard to say. Open box items should be thoroughly checked out before purchase, In my opinion.