This is the 2145th most frequent Russian word.
африканских
"Of African" or "African" (adjective, plural genitive form).
The word 'африканских' functions as an adjective describing the noun 'книг' (books), specifying their origin.
В этой библиотеке много африканских книг.
This library has many African books.
In this sentence, 'африканских' acts as an adjective to 'саваннах' (savannas), identifying their geographical association.
Мы посмотрели документальный фильм об африканских саваннах.
We watched a documentary about African savannas.
Here, 'африканских' describes 'материалов' (materials), signifying their source.