This is the 1144th most frequent Russian word.
омской
"Омской" means "of Omsk," referring to something related to the city of Omsk in Russia.
The word 'Омской' is used here as an adjective to denote location, specifying that the gymnasium is in the city of Omsk.
Я учился в Омской гимназии.
I studied at the Omsk gymnasium.
In this case, 'Омской' serves as an attributive adjective describing the embankment, again relating it to Omsk.
Мы часто гуляли по Омской набережной летом.
We often walked along the Omsk embankment in summer.
Here, 'Омской' modifies 'станции метро' to denote that the metro station belongs to or is in Omsk.