A more thorough explanation:

A passbook is a book that a bank uses to record all the transactions made on a depositor's account. It is also known as a bankbook.

For example, when you deposit money into your savings account, the bank will record the transaction in your passbook. Similarly, when you withdraw money or earn interest on your account, the bank will update your passbook accordingly.

The passbook serves as a record of all the transactions made on your account, and it is important to keep it safe and up-to-date. It can also be used as proof of your account balance when needed.