This is the 2456th most frequent Polish word.
czytelników
"Readers" (genitive plural form).
The word 'czytelników' is the plural genitive form of 'czytelnik', indicating the group of readers associated with the library.
Liczba nowych czytelników naszej biblioteki stale rośnie.
The number of new readers of our library is constantly growing.
Here, 'czytelników' is in the plural genitive form, as it follows the preposition 'dla' (for) which requires it.
Przygotowaliśmy specjalne upominki dla wiernych czytelników.
We prepared special gifts for our loyal readers.
In this instance, 'czytelników' is again in the plural genitive form, used after the possessive pronoun 'naszych' (our).