The body mass index (BMI) is a measure of body fat based on an individual's height and weight. It is calculated by dividing weight in kilograms by the square of height in meters. While BMI provides a quick assessment of whether a person has a healthy weight, it does not directly measure body fat percentage or distribution. As a result, it may not accurately represent the health of all individuals, particularly athletes or those with a muscular build. BMI is a useful screening tool but should be interpreted alongside other health indicators.