This is the 8082nd most frequent Russian word.
курском
"Курском" is the prepositional case of "Курск," meaning "in Kursk" (a city in Russia).
In this sentence, 'Курском' refers to the city Kursk in the locative/prepositional case, indicating location.
Я жил в Курском, когда учился в университете.
I lived in Kursk when I was studying at the university.
Here, 'Курском' describes the factory by specifying its association with Kursk, using the locative case as part of the noun phrase.
Он работает на Курском заводе.
He works at the Kursk factory.
In this sentence, 'Курском' is in the locative case, used to describe the topic of the book, which pertains to the city Kursk.