In simple mans language, diabetes is a lifestyle disorder where the cells in pancrease called islets of langerhans does not produce insulin when required in right quantity to convert the sugar to energy and store it.
Diabetes is a disease that occurs when your blood glucose, also called blood sugar, is too high. Blood glucose is your main source of energy and comes from the food you eat. Insulin, a hormone made by the pancreas, helps glucose from food get into your cells to be used for energy. [Source]
Diabetes can be controlled by leading a disiplined lifestyle and proper medication.