Body mass index (BMI), otherwise known as the Quetelet index, is a measure of tissue mass in the body which includes muscle, fat, and bone. It is expressed as the ratio between the body mass in kilograms divided by the square of the height in m². According to the World Health Organization (WHO), an adult whose BMI is greater than or equal to 30 is considered as obese. Therefore, an individual whose BMI is 42 is classified as obese.