This is the 573rd most frequent Russian word.
квартиры
Apartments or flats.
Here, 'квартиру' is the accusative case of 'квартира', indicating motion to a specific apartment.
Я иду в квартиру, которая находится на первом этаже.
I am going to the apartment that is located on the first floor.
In this sentence, 'квартиры' refers to the plural form, indicating multiple apartments.
Квартиры в этом районе очень дорогие.
The apartments in this area are very expensive.
Here, 'квартиры' is in the genitive case, showing possession or proximity.