An older clinical term for severe obesity, generally describing body weight far above the healthy range, historically around twice ideal body weight and now typically defined as a body mass index of 40 or above. At this level, the risks of type 2 diabetes, cardiovascular disease, sleep apnoea, joint damage, and certain cancers rise steeply, and life expectancy falls. Management requires intensive, multidisciplinary care combining dietary change, physical activity, behavioural support, medication, and, for suitable candidates, bariatric surgery, which produces the most durable results. Modern terminology prefers class III obesity, but the older phrase persists in medical and legal contexts.