Definition of Flag, law of
In maritime law, the law of that nation or country whose flag is flown by a particular vessel. A shipowner who sends his vessel into a foreign port gives notice by his flag to all who enter into contracts with the master that he intends the law of that flag to regulate such contracts, and that they must either submit to its operation or not contract with him.
That's the definition of Flag, law of in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.