Hi,
If referring to the normal weight but metabolically obese individuals, it means people who are not defined as obese by BMI or weight, but have features of the so-called metabolic syndrome (high lipids, high sugar, insulin resistance, high uric acid, high blood pressure, fatty liver; with increased risk for diabetes and heart problems).
Individuals with a belly, a sedentary life or sometimes a genetic predisposition could be included in this category.
Wishing you the best possible health,
Dr Francisco.