BMI, or Body Mass Index, is a widely used tool to assess healthy body weight relative to height. It is calculated using the formula weight in kilograms divided by height in meters squared. BMI is categorized into ranges: underweight, normal weight, overweight, and obese. While it provides a quick method to identify potential health risks associated with body fat, it does not account for muscle mass, fat distribution, or overall fitness level. Thus, while informative, BMI should be used in conjunction with other assessments for a complete evaluation of health.