Cardio is a short term for cardiovascular. Cardiovascular is a term used for the circulatory system consisting of the heart and blood vessels. If you didn't know heart is a muscle and needs to be exercised. If you don't exercised for 20 minutes or longer you have the possibility to get a heart disease. You could get a heart disease because the less you work your heart gets weaker. It doesn't really matter what kind of exercise or activity you do but you need to be moving your whole body.
Some activities that can help your heart keep being healthy are running, hiking, and swimming. All this activities help you because they make your heart works harder. Also while you're working out it's helping you to lose weight.
In order to keep a healthy life you should exercise 2 or 3 days for 20 or 30 minutes. Some activities that I do in my physical education class are play basketball and run. During vacations I'm going to try to join a sport and also i'm going to start doing exercises.