"Diabetes" is a medical term which literally means, 'a metabolic disease which causes excessive thirst and increased production of urine'. In general terms when we talk of 'diabetes' we mean Diabetes Mellitus and it means 'high blood sugar (glucose) .
Glucose is an essential source of energy for our body, but when the levels increase beyond a certain level, it can become harmful and can damage various organs and systems over long time.
Your body changes most of the food you eat into glucose. Your blood takes the glucose to the cells throughout your body. The glucose needs insulin to get into the body's cells. Insulin is a hormone made in the pancreas, an organ near the stomach. The pancreas releases insulin into the blood. Insulin helps the glucose from food get into body cells.
Basically when there is not sufficient insulin level in the blood to help glucose to enter the body cells, or the insulin present is not able to work efficiently to allow glucose from blood to enter body cells, the level of glucose in blood increases above normal levels.
If not controlled, diabetes can lead to blindness, heart disease, stroke, kidney failure, amputations (having a toe or foot removed, for example), and nerve damage. In women, diabetes can cause problems during pregnancy and make it more likely that your baby will be born with birth defects.