Aerobic exercise is anything which raises your heart rate...eg walking, running, swimming etc. Strength training concentrates on building or maintaining muscle....which is better though?
Cardio will burn more calories than strength training, which would explain why people who do aerobic exercise lose more weight on the scales in less time....BUT cardio will burn muscle while strength training will burn fat.
WHY? Because by building more muscle you will burn more fat without even trying. Gain 3lb of muscle and you'll burn approximately 120 calories a day without moving a muscle!