Subsidy : A kind of financial government assistance, such as a grant, tax break, or barrier against competing imports. Subsidies are used to encourage the production or purchase of goods. The term can also refer to other forms of assistance given to individuals or non-government institutions.
Tariff/Duties : A tax on foreign goods charged as they are imported. When a ship arrives in port, a Customs officer inspects the contents and charges a tax according to the tariff formula. Smugglers try to evade tariffs.
Dumping : In international trade, this happens when a country exports a large amount of goods to another country at prices much lower than the prices in the domestic market. This hurts the domestic makers of that product. Therefore, you have anti-dumping tariffs and duties to protect domestic industries.