BMI stands for Body Mass Index, a measurement used to assess body weight in relation to height. It is calculated by dividing an individual’s weight in kilograms by their height in meters squared (kg/m²). BMI provides a simple method to categorize individuals into underweight, normal weight, overweight, or obese categories. Although it's a useful screening tool, it doesn't account for muscle mass or distribution, so additional assessments may be necessary to gain a complete picture of an individual’s health.