In its most extensive sense it means all commerce which is carried on contrary to the laws of the state. This term was also used to designate all kinds of merchandise which were used or transported against the interdictions published by a ban or solemn cry.
During time of war, materials carried aboard a vessel that could aid a belligerent in the process of the war such as arms, weapons or munitions.
The term is usually applied to that unlawful commerce which is so carried on in time of war. Commodities particularly useful in war are contraband as arms, ammunition, horses, timber for ship building, and every kind of naval stores. When articles come into use as implements of war, which were before innocent, they may be declared to be contraband. The greatest difficulty to decide what is contraband seems to have occurred in the instance of provisions which have not been held to be universally contraband, though they may become so on certain occasions when there is an expectation of reducing an enemy by famine.
In fairly modern times one of the principal criteria adopted by the courts for the decision of the question whether any particular cargo of provisions be confiscable as contraband is to examine whether tbose provisions be in a rude or manufactured state; for all articles in such examinations are treated with greater indulgence in their natural condition than when wrought tip for the convenience of the enemy's immediate use. Iron, unwrought, is therefore treated with indulgence, though anchors and other instruments fabricated out of it, are directly contraband.
Contraband of war is the act by which, in times of war, a neutral vessel introduces, or attempts to introduce into the territory of one of the belligerent parties, arms, ammunition or other effects intended for, or which may serve, hostile operations.