What is Defender Of The Faith?

Legal Definition
A peculiar title belonging to the sovereign of England, as that of "Catholic" to the king of Spain, and that of "Most Christian" to the king of Franca These titles were originally given by the popes of Rome; and that of Defensor Fidei was first cohferred by Pope Leo X. on King Henry VIII., as a reward for writing against Martin Luther; and the bull for it bears date quinto Idus Octob., 1521. Enc. Lond.
-- Black's Law Dictionary
Legal Definition
One of the titles of an English king or queen.
-- Ballentine's Law Dictionary