This is the 14019th most frequent Russian word.
овсяные
"Овсяные" means "oat" or "oatmeal" when referring to something made from or related to oats.
Here, 'овсяные' is used as an adjective to describe the type of cookies, indicating they are made of oats.
Я купил свежие овсяные печенья в магазине.
I bought fresh oatmeal cookies at the store.
In this sentence, 'овсяные' qualifies 'хлопья' to denote the kind of flakes, which are oatmeal flakes.
На завтрак я предпочитаю овсяные хлопья с фруктами.
For breakfast, I prefer oatmeal flakes with fruits.
'Овсяные' in this context describes 'поля' to specify that these fields are planted with oats.