Balance of trade can be define as

Balance of trade refers to the difference between the value of a country's imports and the value of its exports over a specific period, usually a year. In other words, it is a measure of the net inflow or outflow of goods and services in and out of a country. If the value of exports is greater than the value of imports, the balance of trade is said to be positive, indicating a trade surplus. Conversely, if the value of imports is greater than the value of exports, the balance of trade is negative, indicating a trade deficit.