This is the 8461st most frequent Polish word.
polskie
"Polskie" means "Polish" (relating to Poland or its people, culture, or language).
Here, 'polskie' is used as an adjective describing the origin or association of the apples with Poland.
To są polskie jabłka.
These are Polish apples.
In this sentence, 'polskie' is an adjective that modifies 'książki' (books), indicating that the books are related to Poland or are in the Polish language.
Kupiłem polskie książki.
I bought Polish books.
'Polskie' in this context describes products that are made in Poland or have characteristics connected to Polish culture or industry.