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.
Tariff
Many countries allow a traveler to bring goods into the country duty-free. These goods may be bought at ports and airports or sometimes within one country without attracting the usual government taxes and then brought into another country duty-free. Some countries impose allowances which limit the number or value of duty-free items that one person can bring into the country. These restrictions often apply to tobacco, wine, spirits, cosmetics, gifts and souvenirs. Often foreign diplomats and UN officials are entitled to duty-free goods. Duty-free goods are imported and stocked in what is called a bonded warehouse.