This is the 8373rd most frequent Russian word.
морской
"Морской" means "marine" or "related to the sea."
Here, 'морской' functions as an adjective describing 'отдых', modifying it to indicate it's related to the sea or ocean.
У нас был чудесный морской отдых на берегу Черного моря.
We had a wonderful seaside vacation on the shore of the Black Sea.
Here, 'морской' modifies 'ветер', specifying that the wind carries characteristics associated with the sea environment.
Морской ветер приносит свежесть и прохладу в жаркие дни.
The sea breeze brings freshness and coolness on hot days.
Here, 'морские' modifies 'деликатесы', suggesting that the delicacies specifically consist of seafood or items derived from the ocean.