Ectomorphic refers to a body type characterized by a slim, lean physique with narrow shoulders and hips. Individuals with this body type typically have a fast metabolism, making it difficult for them to gain weight or muscle mass. Ectomorphs often have long limbs and little body fat, which can give them a delicate appearance. This classification is part of the somatotype theory developed by William Sheldon in the 1940s, which categorizes human bodies into three main types: ectomorphic, mesomorphic, and endomorphic. Understanding these body types can help individuals tailor their fitness and nutrition plans to better suit their natural physique.