The balance of trae (or net exports, sometimes symbolized as NX) is the difference between the monetary value of exports and imports in an economy over a certain period of time. A positive balance of trade is known as a trade surplus and consists of exporting more than is imported; a negative balance of trade is known as a trade deficit or, informally, a trade gap. The balance of trade is sometimes divided into a goods and a services balance; especially in the United Kingdom the terms visible and invisible balance are used.