This is the 1457th most frequent Russian word.
квартире
"Квартире" is the dative or prepositional case of "квартира," meaning "apartment" or "flat" in English.
The word 'квартире' is used in the prepositional case to denote location, indicating where the speaker lives, within an apartment.
Я живу в большой квартире.
I live in a big apartment.
Here, 'квартире' is used in the prepositional case as the location of the activity, specifying that the cleaning is taking place inside the apartment.
Мы убираем в квартире перед праздником.
We are cleaning the apartment before the holiday.
In this example, 'квартире' again appears in the prepositional case, describing where the change in temperature is observed.