Act of State, means not all governmental acts as it does in the French and Continental Systems but only some of them. The term is next used to designate immunities and prohibitions sometimes created by statutes. The term is also extended to include certain prerogatives and special immunities enjoyed by the sovereign and its agents in the business of internal government. the term is even used to indicate all acts into which, by reason that they are official in character, the Courts may not inquire, or in respect of which an official declaration, is bindings on the Courts, State of Saurashrtra v. Meman Haj Ismail, AIR 1959 SC 1383 (1387): (1960) 1 SCR 537.
Means acts done against aliens in exercise of sovereign power of the State. The Municipal Courts debarred from entering into the validity of the Act of State, Secretary of State for India in Council v. Kamachee Boyee Sabha, 7 MIA 476. See also Jahangir v. Secretary of State for India, 6 Bom LR 131; Virendra v. State of Uttar Pradesh, 1955 SCR 415. The arrest of an alien enemy under Defence (General) Regulations, 1939 is not an act of State, Hirsch v.'Somervell, 62 TLR 592; Stroud's Dictionary of Law, Vol. 1, p. 38.
The term Act of State does not always mean a sovereign act against an alien which is neither grounded in law nor does it pretend to be so. The term means more than that because it has many meanings, Roman Cathelic Mission v. State of Madras, AIR 1966 SC 1457 (1464): (1966) 3 SCR 283.
The expression 'Act of State' is not limited to hostile action between rulers resulting in the occupation of territories. It includes all acquisitions of territory by a sovereign State for the first time, whether it be by conquest or cession, Dalmia Dadri Cement Co. Ltd. v. CIT, AIR 1958 SC 816 (822).
The Act of the sovereign power of a country or its agent (if acting intra vires). By its very nature
such an act cannot be questioned by any Court of Law.
An 'Act of State' is an act done in relation to a foreigner by the sovereign power of a country or its agent either previously authorised or subsequently ratified. Such an act cannot be questioned or made the subject of legal proceedings in any Court of law, B.K. Mohapatra v. State of Orissa AIR 1988 SC 24 (28): (1987) Supp SCC 553.
In International Law, means the uncontrolled exclusive exercise of powers of a State, that is, both of the power of entering into relations with other States, and of the power of governing its own subjects. Dictionary of Law, William C. Anderson, 1889, p. 960.