It's a tax levied by a government usually on imported goods. A country produces a certain type of goods. Another country produces the same goods for less. When the imported good are sold, they are sold for less than the domestically produced goods sell for. The local manufactures loose sales to the imported goods. The government of the importing country applies a tariff to the imported goods raising their prices, and now that the imported goods cost more, the local goods have a better chance of competing for sales. This is why it is called a "protective" tariff, because it is protecting the local industry.
