"Ad Valorem" is a word in LAW AND LEGAL, ENGLISH

According to value. Duties are either ad valorem or speei/fc; the former when the duty Is laid in the form of a percentage on the value of the property; the latter where It ls imposed as a fixed sum on each article of a class without regard to its value. The term ad valorem tax ls as well defined and fixed as any other used in political economy or legislation, and sim-ply means a tax or duty upon the value of the article or thing subject to taxation. Bailey v. Fuqua, 24 Miss. 501; Pingree v. Auditor General, 120 Mich. 95, 78 N. W. 1025, 44 L. R. A. 679

A term used to denote a duty or charge laid upon goods,
at a certain rate per cent upon their value, as stated in their
invoice, -- in opposition to a specific sum upon a given quantity or
number; as, an ad valorem duty of twenty per cent.