Objectives : In Huangdineijing(黃帝內經), there are many uncertain terms to express body structures, for example, Yuk(肉, flesh). The purpose of this study is to define the meaning of Yuk(肉, flesh) and relevant terminologies. Methods : To define the meaning and origin of Yuk(肉) character and relevant terminologies, examples in Huangdineijing(黃帝內經), Seolmunhaeja(說文解字) and other important references are investigated. Results : Yuk(肉) character has etymologically meant meat, and afterwards it has got meaning of flesh. In the main two terms derived from Yuk, Giyuk(肌肉) means flesh, and Bunyuk(分肉) means muscles in anatomical knowledges. Also Yuk has been the most important etymological word that means body, among the five parts of body[五體], Geun(筋, tedndon and ligament), Maek(脈, blood vessel), Yuk(肉 flesh), Pi(皮, skin) and Gol(骨, bone) to contribute to making basic meanings of those characters. Conclusions : It is necessary to make clear the definitions of many Korean medical terminologies especially in anatomical knowledges to be helpful for systematic management of terminologies.