An insulin pump sends a constant dose of basal insulin into your body 24 hours a day through a plastic tube and a small needle that you insert in your skin. When you need extra insulin, such as after you eat, you can give yourself an extra dose by pressing buttons on the pump. You can clip the pump to your belt or carry it in your pocket. Or you can wear the pump on a special belt like the one in this picture.
WebMD Medical Reference from Healthwise