Bank Statement is a copy of a customer account in the bank book. It is a document provided by the bank to its customers, which shows all the transactions that have taken place in the customer's bank account over a specific period of time. It is an important financial document that helps the customer reconcile their own records with the bank's records.

**Explanation:**

**1. Definition of a Bank Statement:**
A bank statement is a summary of all the transactions that have occurred in a bank account during a specific period of time. It is typically issued by the bank at the end of each month, but can also be obtained on demand.

**2. Purpose of a Bank Statement:**
The main purpose of a bank statement is to provide the account holder with an accurate record of all the transactions that have taken place in their bank account. It allows them to verify the accuracy of their own records and ensure that there are no discrepancies or errors.

**3. Contents of a Bank Statement:**
A bank statement typically includes the following information:
- Account holder's name and address
- Account number
- Statement period (start and end date)
- Opening and closing balances
- Individual transaction details (debit and credit)
- Cheque numbers (if applicable)
- Bank charges and fees (if applicable)
- Interest earned (if applicable)

**4. Relationship with the Bank Book:**
The bank statement is a copy of the customer account in the bank book. The bank book is a record maintained by the bank, which contains all the transactions related to the customer's account. It includes deposits, withdrawals, cheques issued, cheques deposited, and other relevant information.

The bank statement provides a summarized version of the bank book, highlighting the opening and closing balances, as well as the individual transaction details. It acts as a proof of the transactions that have taken place and serves as a reference for the account holder to reconcile their own records with the bank's records.

**Conclusion:**
In conclusion, a bank statement is a copy of a customer account in the bank book. It provides a summary of all the transactions that have occurred in the customer's bank account over a specific period of time. It is an important document for account reconciliation and helps ensure the accuracy of the customer's financial records.