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.
Protective tariff
Protective tariffs are tariffs that are enacted with the aim of protecting a domestic industry. They aim to make imported goods cost more than equivalent goods produced domestically, thereby causing sales of domestically produced goods to rise; supporting local industry. Tariffs are also imposed in order to raise government revenue, or to reduce an undesirable activity (sin tax). Although a tariff can simultaneously protect domestic industry and earn government revenue, the goals of protection and revenue maximization suggest different tariff rates, entailing a tradeoff between the two aims.