Not all treasure is silver and gold, mate.
An unmatched book is an imbalance that occurs when the maturity of a bank’s assets, such as loans, does not match the maturity of its liabilities, such as interest-paying accounts, on the balance sheet. When the maturity of liabilities is shorter than the maturity of assets, the payments associated with the liabilities will come due, but income from the assets may not yet be available due to the longer maturity date. This is the opposite of asset/liability matching, where the maturities of assets and liabilities are the same. When an asset matures, the cash is used to pay the associated cash flow for the liability.