The Sheldon scale is a system used to categorize human body types based on physical characteristics. Developed by psychologist William Herbert Sheldon in the 1940s, it classifies individuals into three primary somatotypes: ectomorph, mesomorph, and endomorph. Each type reflects different physical traits, such as body fat, muscle mass, and bone structure. Ectomorphs are typically slim and lean, mesomorphs are muscular and well-proportioned, while endomorphs tend to have a rounder physique with more body fat. The Sheldon scale has been influential in fields like psychology and fitness, helping to understand how body types can affect personality and health.