HIIT stands for High-Intensity Interval Training. It's a form of cardiovascular exercise that alternates between short bursts of intense anaerobic exercise and periods of less intense recovery or rest. HIIT workouts are known for their effectiveness in burning calories, improving cardiovascular health, and increasing metabolism in a shorter amount of time compared to traditional steady-state cardio exercises. They can include a variety of exercises such as sprints, jumping jacks, burpees, and high knees, among others.