This is a legal term used in international law. It means that something that falls outside international boundaries and is considered to be a common good to many nations (like a population of endangered migratory animals or an unclaimed territory like Antarctica) is entirely subject to international controls in the sense that a nation is not supposed to take an action affecting the subject (like, for instance, setting up a mining facility in Antarctica) unless the rest of international community positively and officially agrees to the action.