Arrears
From ACT Wiki
1.
Payments made 'in arrears' are the opposite of ones paid in advance.
For example, quarterly payments in arrears, over a 12-month period, would be paid at the ends of months 3, 6, 9 and 12.
If the payments had been made 'in advance' the first payment would instead be at the start of the year, with the three subsequent payments being 3, 6 and 9 months later.
2.
'Arrears' can also mean amounts owing and not yet paid, which should already have been paid.
A borrowing (or other obligation) which is 'in arrears' in this sense means that the borrower (or other obligor) has not met their agreed schedule of payments.
In banking, the related customer account is said to be 'delinquent'.
