This is the 2706th most frequent Russian word.
брянской
"Брянской" means "Bryansk" as an adjective, relating to Bryansk, a city or region in Russia.
Indicating location or origin, 'брянской' is in the genitive singular case to agree with the noun 'область' (region).
Я посетил брянской область летом.
I visited the Bryansk region in the summer.
Using 'Брянская' as an adjective to describe the region's proper name, indicating 'of Bryansk'.
Брянская область известна своими густыми лесами.
The Bryansk region is known for its dense forests.
Here, 'Брянскую' is in the accusative singular case, agreeing with the preposition and noun it modifies.