The real wordsTheory
Salvatore's definitions
Balance of paymentsa summary statement of the international transactions of a nation for a specified period of time.
International transactionthe exchange of a good, service or asset between residents of one nation and residents of another.
The purpose is stated plainly on the slide: to help the government in formulating monetary, fiscal and trade policies. Learn that clause; it is a one-mark question on its own.
The student's note adds that some entries involve no foreign resident directly, for instance a central bank selling its foreign currency holdings to commercial banks.