This is the 882nd most frequent Polish word.
ostrołęce
"Ostrołęce" is the locative form of "Ostrołęka," a city in Poland, used to indicate location or context related to it.
The term 'Ostrołęce' is used here to denote the location (a city in Poland) where the speaker's grandparents live, including the grammatical locative case to indicate the place of an action.
W Ostrołęce mieszkają moi dziadkowie.
My grandparents live in Ostrołęka.
Here, 'Ostrołęce' refers to the city mentioned as a past destination, also using the locative case to indicate being at this location.
Byłem kiedyś w Ostrołęce na wakacjach.
I was once in Ostrołęka for vacation.
In this sentence, 'Ostrołęce' indicates the meeting location, employing the locative case which is common in Polish for such references.