outstanding; unsettled; unpaid
Used in accounting and finance for accounts, payments, or transactions that have not yet been settled or cleared.
There are still outstanding invoices.
Please check the unsettled transactions.
決済 means 'settlement' or 'payment completion'; 未決済 is its negative form indicating the settlement has not yet occurred.
Compound of 未 (mi, 'not yet') + 決済 (kessai, 'settlement, payment').