Body composition refers to the proportion of fat and fat-free mass (muscle, bones, organs, and water) in the body, whereas weight simply measures overall mass without distinguishing between fat and muscle. Understanding body composition is important for assessing health and fitness levels, as a higher muscle mass relative to body fat can indicate better overall health and physical capability. Weight alone can be misleading, as factors such as muscle gain and fat loss may not alter the scale despite positive changes in body composition.