This is the 12287th most frequent Russian word.
истекшую
"Expired" or "elapsed."
Here, 'истекшую' is used as an adjective describing the debt that has expired or passed its period of validity.
Он оплатил истекшую задолженность.
He paid off the expired debt.
In this case, 'истекшую' describes the date that has passed, referring to a deadline that has expired.
Договор истекшую дату был аннулирован.
The contract was annulled on the expired date.
Here, 'истекшую' is used to describe a product whose validity, like a shelf life or usage period, has passed.