BMI, or Body Mass Index, is a numerical value derived from a person's weight and height. It is calculated by dividing a person's weight in kilograms by the square of their height in meters. This measurement helps categorize individuals into different weight status groups, such as underweight, normal weight, overweight, and obesity. BMI is widely used as a simple screening tool to assess whether a person has a healthy body weight for their height. However, it does not directly measure body fat or account for factors like muscle mass, age, or gender, which can influence overall health.