This is the 14925th most frequent German word.
russisch
"Russisch" means "Russian" in English.
In this case, 'russisch' is used as an adjective to describe the origin or attribute of the book.
Das ist ein russisches Buch, das ich kürzlich gekauft habe.
This is a Russian book that I recently bought.
Here, 'russisch' is used as an adjective modifying 'Kultur' to specify that the culture discussed is Russian.
Die russische Kultur ist bekannt für ihre Vielseitigkeit und Tiefe.
Russian culture is known for its diversity and depth.
Here, 'russisch' is used as an adverb to indicate the action of learning the Russian language.