BMI, or Body Mass Index, is a measurement used to evaluate body weight relative to height. It is calculated by dividing a person’s weight in kilograms by the square of their height in meters (kg/m²). BMI categories determine whether a person is underweight, normal weight, overweight, or obese. While it is a useful screening tool for assessing potential health risks associated with body weight, it does not account for muscle mass or body composition, so it should be considered alongside other health metrics.