What is a book in money?

Could you please elaborate on the concept of "a book in money"? I'm intrigued by this phrase as it's not a commonly used term in financial or cryptocurrency circles. Are you referring to a ledger or a record of transactions, akin to the books that banks or financial institutions keep to track the movement of funds? Or is it something more specific to cryptocurrency, such as a blockchain or a decentralized ledger that tracks the ownership and transfer of digital assets? I'd appreciate any clarification you can provide.