High in fat, salt or sugar (HFSS) is the regulatory shorthand — used in UK food policy — for products whose content of these nutrients exceeds set thresholds, marking them as less healthy. The HFSS classification underpins some of Britain’s toughest food regulations: restrictions on advertising such products to children, on their promotion by multibuy deals and prominent store placement, and nutrient-profiling rules for what may be marketed as healthy. The thresholds use a scoring system weighing negative nutrients against positive ones like fruit, vegetable, fibre, and protein content. Industry has responded with widespread reformulation — cutting sugar, salt, and fat to escape the HFSS net — making the definition a genuine lever on the food supply.