Reactive oxygen species (ROS) is loosely synonymous with "free radicals", which is more of an older term. ROS include free radical oxygen, but also other energetic non-radical species such as singlet oxygen and peroxide ions.

But yeah, your broad point is correct. Biology has several billions of years of evolutionary experience dealing with ROS and upregulates antioxidant biomolecules in response, it's way more complex than "ROS bad".