High Intensity Interval Training (HIIT) is a form of cardiovascular exercise that consists of quick but intense bursts of activity that use 100% of your effort and tire your muscles out in a shorter period of time. HIIT bursts usually last for a minute or less and are alternated with brief, low intensity recovery periods.
This sequence is then repeated for approximately 4-20 minutes. Performing HIIT cardio two to three times per week is far more effective than traditional, steady state cardio when it comes to burning fat: it accelerates your metabolism, improves muscle endurance (making both your muscles and heart stronger!), cardiovascular conditioning and athletic performance.
In other words, HIIT emphasizes the quality of the exercise, rather than the time or quantity.
The types of exercises you incorporate into your HIIT routine are up to you. I have clients that prefer burpees, push-ups, sit ups, planks, or other functional moves. Try to incorporate compound moves that use multiple major muscle groups for maximum effectiveness!