BMI, or Body Mass Index, is a numerical value derived from an individual's weight and height, calculated as weight in kilograms divided by height in meters squared. It is crucial in assessing health status as it provides a simple method to categorize individuals into underweight, normal weight, overweight, or obese. Although BMI does not directly measure body fat, it serves as a useful screening tool to identify potential health risks associated with excess weight, such as heart disease and diabetes.