BMI stands for Body Mass Index. This value comes from the weight or mass of a person and their height or how tall they are. To define this term, it strictly means that the body mass is divided by the body height. Most of the time the body mass index is measured in kilograms over meters squared. The mass is measured in the kilograms and the height is measured in meters.
If you are wondering what is a healthy BMI for a person, you can calculate it. Then, you have a low BMI if your number if under 18.5. It is average if it falls between 18.5 and 25. It is high if your number is over 25. There are exceptions to the BMI due to gender and race.