This is the 17282nd most frequent Polish word.
zaległym
Overdue.
In this sentence, 'zaległym' is used as an adjective describing the noun 'rachunek' (bill), indicating something past due or overdue.
Mam do zapłacenia zaległy rachunek.
I have an overdue bill to pay.
Here, 'zaległe' is the plural form of the adjective 'zaległy', describing 'sprawy' (matters), reflecting something postponed or not addressed yet.
Podczas zebrania omawialiśmy zaległe sprawy.
During the meeting, we discussed overdue matters.
In this context, 'zaległym' describes 'projektem' (project) and implies a task or obligation not completed on time.