Cardio is exercise that increases your heart rate: It gets your blood pumping. A little cardio, such as jogging or even dancing, can do a lot to keep your heart healthy as you age.
Cardio means "heart," but it's used as shorthand for any exercise that works out your cardiovascular system, which includes the heart and blood vessels. Aerobic exercise, which increases how fast you breathe due to your body's need for more oxygen, is cardio, because when you breathe more, your heart pumps more. Aerobics and cardio are often used interchangeably. The term cardio is also an adjective that refers to anything related to the heart or to exercise that gives the heart a workout.