This document defines diabetes mellitus as a metabolic disorder resulting from defects in insulin secretion or action. It describes the two main types of diabetes - type 1 caused by pancreatic beta cell destruction and type 2 related to insulin resistance. Symptoms, complications, and diagnostic tests are outlined, including fasting blood glucose, oral glucose tolerance test, and HbA1c. The goals of treatment are to control blood glucose levels and minimize long-term complications through lifestyle changes and medication if needed.