Trade:

Trade refers to the voluntary exchange of goods or services between different economic actors. Since the parties are under no obligation to trade, a transaction will only occur if both parties consider it beneficial to their interests.

Aid:

foreign aid is the international transfer of capital, goods, or services from a country or international organization for the benefit of the recipient country or its population. Aid can be economic, military, or emergency humanitarian (e.g., aid given following natural disasters).

Exchange:

exchange, international exchange also called foreign exchange, respectively, any payment made by one country to another and the market in which national currencies are bought and sold by those who require them for such payments.