Aerobic
The term aerobic refers to the type of energy metabolism carried out by your body in the presence of oxygen. Aerobic metabolism, or aerobic oxidation sustains exercise for longer durations of time. The aerobic system uses stored fats, carbohydrates (glycogen), and proteins as energy sources.
As the intensity level of exercise increases, the body must rely more upon anaerobic metabolism to meet its pressing energy needs.
Keep in mind that the different types of energy systems used by the body to fuel exercise are not mutually exclusive. They all operate during exercise but to differing degrees depending upon the intensity of the exercise.