Polyunsaturated describes fats and oils that come mainly from plants — sunflower, soya, corn, many seed oils — and that food advice has long called better for the heart than saturated fat from animals. You will see polyunsaturated fat, polyunsaturated oil, polyunsaturated fatty acids (sometimes written PUFA). Omega-3 and omega-6 oils sit in this family. It is a nutrition-label and doctor-leaflet adjective, a bit formal, very common on bottles and boxes. Next to it on the same label you often get saturated (the “full,” often animal kind) and monounsaturated (olive oil is the famous one: one “not-full” place, not many). Though actually, “better than butter” was a loud, simple story, and researchers still fight about how simple it should be. For a student, the useful picture is: this word flags a plant-oil kind of fat, not a plastic, and not “all vegetables are healthy.” Deep-fried food can still be polyunsaturated and still be a poor everyday choice.