terra nullius

Marie Byrd Land, the only unclaimed sector of Antarctica.

Terra nullius (/ˈtɛrə ˈnʌliəs/, plural terrae nullius) is a Latin expression meaning "nobody's land". Since the nineteenth century, it has been used to refer to the principle in international law by which states may acquire land that is not possessed by any other state through the occupation of it. Today Antarctica remains as the only major landmass that is sometimes considered to be wholly or partially terra nullius. Other territories sometimes claimed to be terra nullius include Bir Tawil, a strip of land between Egypt and Sudan, and four pockets of land on the banks of the Danube, on the Croatia-Serbia border; both due to border disputes where both competing claims involve assigning a particular piece of territory to the other party.