Fat-free is a food-label word. It tells you the food is sold as containing no fat — fat-free milk, fat-free yogurt, a fat-free dressing. Shops and packet-writers love it because it sounds clean and careful. Though actually, ‘no fat’ on a packet is often a legal kind of ‘almost none’, not a scientist’s perfect zero: a tiny bit may still be allowed. And fat-free does not mean ‘good for you’, and it does not mean ‘no energy’. Makers often add sugar, salt, or starch so the food still tastes like something. People who are watching fat will look for this word; people who are watching sugar may need to turn the packet over. It is everyday and commercial, not poetic. You can put it before a noun (fat-free yogurt) and, a little more loosely, after a verb (this yogurt is fat-free).