In health and fitness contexts, the letters BMI stand for Body Mass Index. BMI is a numerical value derived from an individual's weight and height, serving as a simple method for categorizing individuals into different weight classifications, such as underweight, normal weight, overweight, or obese. While it can provide a quick assessment of body fatness and is useful in population studies, it does not directly measure body fat or consider factors like muscle mass, age, and gender. Despite its limitations, BMI is commonly used to assess health risks associated with weight.