Overweight means an excess of total body weight based on population averages for heights and body frame sizes. Athletes and very muscular people may be overweight, but that does not mean they are over fat. Obesity means an excess of body fat regardless of weight.
 

Men A, B and C are exactly the same height. A and B have the same weight, and C weighs considerably more. For his height C appears to be fat. But after analyzing body fat levels, B and C have acceptable percentages while A has above the recommended range and is at a higher health risk.