What is Act Of Law?

Legal Definition
The operation of fixed legal rules upon given facis or occurrences, producing consequences independent of the design or will of the parties concerned; as distinguished from "act of parties." Also an act performed by judicial authority which prevents or precludes a party from fulfilling a contract or other engagement. Taylor v. Taintor, 16 Wnil. 366, 21 L. Ed. 287.
-- Black's Law Dictionary
Legal Definition
Operation of law.
-- Ballentine's Law Dictionary