In medical terms, "DM" stands for diabetes mellitus. Diabetes mellitus is a term that refers to type 1 or type 2 diabetes, as stated by MedicineNet.
Type 1 diabetes is a chronic disease that occurs when the pancreas produces little or no insulin due to the destruction of insulin-producing beta cells. This disease commonly develops in children and adolescents, but it may also develop in adults. Patients must take daily insulin injections to regulate their blood glucose, according to MedicineNet.
Type 2 diabetes occurs when the body's cells become resistant to insulin, which the cells require in order to access glucose for energy. This disease may be treated with exercise, diet and weight loss. Oral medications or insulin may be required if the other methods fail to control blood glucose levels.