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.
Import Surtaxes
Import surtaxes, also known as special tariffs, are extra taxes on top of the normal import tax of imported goods, with the extra taxes being reserved for some purposes. They are different from import duty, which is not reflected in the customs tariff and is set for a specific purpose. Often, they depend on their level of taxation, which is the specific purpose for their collection. They are usually temporary or one-off.