Tariff
A tariff is called an optimal tariff if it's set to maximize the welfare of the country imposing the tariff. It is a tariff derived by the intersection between the "trade indifference curve" of that country and the offer curve of another country. In this case, the welfare of the other country grows worse simultaneously, thus the policy is a kind of "beggar thy neighbor policy". If the offer curve of the other country is a line through the origin point, the original country is in the "condition of a small country", so any tariff worsens the welfare of the original country.
History of tariffs in Australia
From the point of view of the form and structure of tariffs, the colonial systems had developed features which carried over to the first Australian Customs Tariff. This applied to the mix of specific and ad valorem rates, the more favorable tax treatment of intermediate inputs, the complex differentiation of tariff rates within product groups or industries, and to differential rates on imports of excisable items and the excise tax rates on similar domestic products, which gave a protective margin to imports of alcoholic beverages and tobacco.