Body Mass Index (BMI) is a measurement that uses your height and weight to estimate body fat. It's calculated by dividing your weight in kilograms by your height in meters squared (kg/m²). BMI is widely used as a screening tool to categorize individuals as underweight, normal weight, overweight, or obese.

According to the WHO, a healthy BMI range for adults is 18.5-24.9. BMI categories are: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obese (30 and above). However, these ranges may vary slightly based on age, gender, and ethnicity.

BMI matters because it's associated with health risks. Higher BMI values are linked to increased risk of heart disease, diabetes, high blood pressure, and certain cancers. While not perfect, BMI serves as a useful initial assessment tool for healthcare providers to identify potential health concerns and guide further evaluation.

BMI has several limitations: it doesn't distinguish between muscle and fat mass, may not be accurate for athletes with high muscle mass, doesn't account for fat distribution, and may not be suitable for certain ethnic groups, elderly individuals, or children. It's best used alongside other health assessments rather than as a standalone diagnostic tool.