Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. It is used to assess whether an individual has a healthy body weight for their height. The formula for BMI is weight in kilograms divided by height in meters squared. BMI categories include underweight, normal weight, overweight, and obesity. These classifications help identify potential health risks associated with being underweight or overweight. However, BMI does not directly measure body fat and may not accurately reflect the health of all individuals, such as athletes with high muscle mass.