Subsidiary books are the book of original entry and it is called primary records because the first entry of transaction is made in subsidiary books
Thus book-keeping means recording, classifying and summarizing business transactions systematically so that the businessman may be able to know his profit or loss during a specified period.
Business transactions refer to activities and events that affect the financial position of a business and are capable of being assigned monetary values. Business transactions are recorded in the books of the business and summarized in financial reports.