"High Knees" is a video demonstrating a cardiovascular exercise where you alternately lift each knee towards the chest while jogging in place. This exercise targets the quadriceps, hamstrings, and hip flexors, while also engaging the core muscles for stability and balance. The video typically emphasizes maintaining a fast pace, proper form with high knee lifts, variations, and the benefits of incorporating high knees into a warm-up, cardio routine, or interval training to enhance leg strength, agility, and cardiovascular endurance.