Final answer:
The 'book of original entry' is known as business event data. It's the foundational record in accounting where transactions are initially recorded.
Step-by-step explanation:
According to the text, the "book of original entry" is referred to as A.business event data. This is where all transactions are initially recorded before they may be later summarized and recorded in detail in ledgers. This concept is essential in the field of accounting, as it ensures that each financial transaction is captured completely and chronologically. The book of original entry provides a clear trail of all the economic activities of a business.