visible trade (GB) or merchandise trade (US)
trade in goods
invisible imports and exports
trade in services (banking, insurance, tourism, and so on)
barter or counter-trade
direct exchanges of goods, without the use of money
balance of trade
the difference between what a country receives and pays for its exports and imports of goods
balance of payments
the difference between a country's total earnings and its total expenditure on imports
autarky
the (impossible) situation in which a country is completely self-sufficient and has no foreign trade
surplus
a positive balance of trade or payments
deficit
a negative balance of trade or payments
dumping
selling goods abroad at (below) cost price
protectionism
imposing trade barriers in order to restrict imports
tariffs
taxes charged on imports
quotas
quantitative limits on the import of particular products or commodities