HIIT stands for Hyper Intensity Training, which is primarily short, intense bursts of cardio followed by a brief period of rest. This form of exercise has a very positive effect on your metabolism, heart, and lungs, even after only a few minutes. With interval training, you will often improve cardio function and stamina by doing repetitions, rounds, and sets as your body are hard at work.
High-intensity exercising is not a casual walking workout. However, you should only push just a little bit past your comfort zone to avoid any injuries. You can use HIIT with any cardio exercise. This HIIT could be running, doing the elliptical, bicycling, and swimming.