What is Ante Natus?

Legal Definition
Born before. A person born before another person or before a particular event. The term is particularly applied to one boro in a country before a revolution, change of government or dynasty, or other political event, such that the question of his rights, status, or allegiance will depend upon the date of his birth with reference to such event. In England, the term commonly denotes one barn before the act of union with Scotland; in America, one born before the declaration of independence. Its opposite is post natus, one born after the event.
-- Black's Law Dictionary