BMI stands for Body Mass Index, a measurement used to assess body weight relative to height. Calculated by dividing a person's weight in kilograms by the square of their height in meters, BMI helps categorize individuals into different weight categories, such as underweight, normal, overweight, or obese. While BMI is a useful screening tool, it does not consider factors like muscle mass or distribution, thus it should be used in conjunction with other assessments for a comprehensive view of health.