I would consider yoga to be more of an exercise.  I always leave with a nice sweat and I think it pushes you.  Yoga can be empowering because most of the time you are focused on your breath so your not thinking about all the things that may stress you out.  It allows you to clear your head and go back to reality with fresh thoughts.  Yoga is a different type of exercise than things like running or zumba because it opens up your body and can relax you.