The trade balance is the difference between the value of a country’s exports and imports of goods, or of goods and services, over a period. It is a statistical aggregate compiled under national accounting conventions. The point worth holding on to is that a deficit is one side of an accounting identity: it is matched by a corresponding net inflow on the financial account, and it records that a country is buying more from abroad than it sells — not that it has been treated unfairly or that its policy has failed. Balances also move with exchange rates, commodity prices and the business cycle. Read it as a measurement, not a verdict.
Why this entry carries no source list. This is an analytical concept from economics, not an instrument any body administers. There is no authority to cite because none is needed: the idea is used to reason about trade, not applied by a customs officer to a consignment. Where numbers are involved they come from statistical compilations whose conventions differ, so figures from two sources are not automatically comparable.