Non-performing loan on which interest is overdue and full collection of principal is uncertain. According to typical banking regulations, if interest has not been paid for 90 days the loan is put on a cash basis. Thus, its interest cannot be credited to the bank's revenue account until it has actually been received. Loans which have adequate collateral (such as home mortgages), and some types of consumer loans, are generally exempt from this requirement. Also called doubtful loan, sour loan, troubled loan.