Learner's definition of ARREARS
money that is owed and that has not been paid when it should be
— used to describe a situation in which someone has failed to make a regular payment at the required time
He is two months in arrears [=behind] with his mortgage payments.
The account is two months in arrears. [=overdue, delinquent]
He has fallen into arrears on his mortgage payments.
— used to describe a situation in which someone is paid money that was earned at an earlier time