HIIT stands for High intensity interval training, which consists of short sprint intervals coupled with low-moderate intensity work. An example of this would be a 30 second sprint followed by a 4 minute steady pace walk to cool down and bring your heart rate back to normal and then repeating it. LISS stands for Low intensity steady state cardio, which consists of purely low-moderate intensity work. An example of this would be walking on the treadmill or riding the bike and being able to hold a conversation (we tend to see a lot of this at gyms).