In the simplest terms . . . diabetes mellitus (commonly referred to as just "diabetes") is a blood sugar disease . . . a disease in which the body either does not produce or does not properly utilize insulin.
Insulin is a hormone that is needed to convert sugar, starches and other food into energy needed for daily life. Because diabetics have a problem with insulin, their body's can't use glucose (blood sugar) for energy, which results in elevated blood glucose levels (hyperglycemia) and the eventual urination of sugar out of their bodies. As a result . . . diabetics can literally starve themselves to death.