This is the 10088th most frequent Russian word.
балтийских
"Балтийских" translates to "Baltic" (relating to the Baltic region).
The word 'балтийских' is used as an adjective modifying 'стран', indicating the geographic association of the countries.
Балтийских стран объединяет одно море.
The Baltic countries are united by one sea.
Here, 'балтийских' is an adjective describing 'берегах', denoting the geographical location of the shores.
Она мечтает о путешествии по балтийских берегах.
She dreams of a journey along the Baltic shores.
In this sentence, 'балтийских' acts as an adjective modifying 'регионов'. It refers to the regions associated with the Baltic.