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.
Immigration tariff
An immigration tariff is a charge levied on immigrants wanting permanent residency within a nation. As a means of applying price theory to a nation's immigration policy, it is generally advocated as an alternative to existing bureaucratic procedures as a means of moderating or better regulating the flow of immigration to a given level.