What is Quod Nullius Est, Id Ratione Naturali Occupanti Conceditur?

Legal Definition
That which Is the property of no one is, by natural reason, given to the [first] occupant. Dig. 41, 1, 3; Inst 2, 1, 12. Adopted in the common law. 2 BL Comm. 258.
-- Black's Law Dictionary
Legal Definition
That which belongs to no one, by natural reason is yielded to the occupier thereof.
-- Ballentine's Law Dictionary