BMI stands for Body Mass Index, and it is used to categorize people as underweight, normal weight, overweight, or obese. It is a screen for weight categories that may lead to health problems but it is not diagnostic of the overall health of an individual. A BMI of less than 18.5 means that a person is underweight. A BMI of between 18.5 and 24.9 is ideal. A BMI of between 25 and 29.9 is overweight. A BMI over 30 indicates obesity.
BMR stands for Basal Metabolic Rate, and it is the rate at which your body consumes calories while at rest. If you were to lay in bed all day and do nothing except read, your BMR is the number of calories that your body would burn that day as a result of natural processes like breathing, circulating blood, regulating your body temperature, and even moving your eyes across the pages as you read. Your BMR is used to calculate the number of calories you need each day in order to lose weight, maintain weight, or gain weight.