HIIT is short for High Intensity Interval Training. It is a training protocol alternating short periods of intense or explosive workouts with brief recovery periods until the point of exhaustion. The exercise usually last about 10 to 30 minutes.
HIIT allows you to burn calories at a faster rate in a short amount of time. Muscle gain will slightly be noticeable, but the main goal for this exercise is weight loss. No equipment are necessary when doing these types of workout. You will notice a substantial boost in your metabolism, and build a healthier heart.
HIIT is pretty challenging on the body considering that it requires you to put in 80-90% effort to exercise in a short duration. Only little breaks are provided, but you're attempting this to loss weight and build more resistance with more practice.