This is the 18463rd most frequent Russian word.
югославской
"Yugoslav" – relating to Yugoslavia.
Here, 'югославской' modifies 'эпохи' (era), indicating the time period associated with Yugoslavia.
Этот музей содержит югославской эпохи предметы искусства.
This museum contains objects of art from the Yugoslav era.
The word 'югославской' is used as an adjective describing the noun 'культуре' (culture), referring to something related to Yugoslavia.
В старой библиотеке я нашел книгу о югославской культуре.
In the old library, I found a book about Yugoslav culture.
In this sentence, 'югославской' is an adjective describing 'истории' (history), pointing to historical events or aspects associated with Yugoslavia.