Wiktionary
n. empty land; land not legally belonging to anyone.
Wikipedia
Terra nullius (, plural terrae nullius) is a Latin expression deriving from Roman law meaning "nobody's land", which is used in international law to describe territory which has never been subject to the sovereignty of any state, or over which any prior sovereign has expressly or implicitly relinquished sovereignty. Sovereignty over territory which is terra nullius may be acquired through occupation, (see reception statute) though in some cases doing so would violate an international law or treaty. Terra nullius is derived from the 1095 papal bull, Terra Nullius, of Pope Urban II, which allowed Christian European states to claim land inhabited by non-Christians. That was clearly intended to establish a legal framework for the First Crusade, launched a few years later, and for the conquest of Muslim lands and the establishment on them of the Crusader Kingdoms.
Usage examples of "terra nullius".
At the moment it was terra nullius in the sense that it was newly emerged and open to occupation by anybody.
Red Creek turned out to be an Aboriginal reserve in Australia's Northern Territory, reinstated by the Terra Nullius national government.