In the fitness world, "cardio" refers to cardiovascular exercise, which is any activity that raises the heart rate and improves overall heart health. This includes exercises like running, cycling, swimming, and rowing. Cardio is essential for improving aerobic capacity, burning calories, and enhancing endurance. Regular cardiovascular exercise can lead to significant health benefits, including better weight management, improved mood, and reduced risk of chronic diseases. It is often a fundamental component of many fitness programs.