BMI stands for Body Mass Index, a measurement that evaluates an individual's body weight relative to their height. It is calculated by dividing a person's weight in kilograms by the square of their height in meters. BMI is commonly used as a screening tool to categorize individuals as underweight, normal weight, overweight, or obese, which can help assess potential health risks associated with body weight. While BMI is useful for population studies, it does not directly measure body fat percentage or account for factors such as muscle mass and distribution.