a crystalline substance, CHNO, present in muscle tissue, usually in the form of phosphocreatine
See creatine in American Heritage Dictionary 4
(krēˈə-tēnˌ, -tĭn) also cre·a·tin(-tĭn)
noun
A nitrogenous organic acid, C4H9N3O2, that is found in the muscle tissue of vertebrates mainly in the form of phosphocreatine and supplies energy for muscle contraction.