A quadrillion is a very large number that is equal to 1,000 trillion or 1 followed by 15 zeros: 1,000,000,000,000,000. In the metric system, it is represented as 10^15. This number is often used in fields like science and finance to describe extremely large quantities, such as the total number of stars in a galaxy or the national debt of a country like the United States. To put it into perspective, if you had a quadrillion dollars, you could spend a million dollars every day for over 2,700 years! This shows just how massive a quadrillion really is, making it hard to imagine in everyday life.