What is the difference between cardio and aerobic exercise?

It is and it isn't. It completely depends on what your aim is i.e loose weight, get aerobic fit or cardio fit! In themselves they are quite different. We all know what cardio is and its usually done for longer periods of time . . . while sport aerobics is high intensity and not for as long. So it practically depends on the individual and his or hers needs. :)