A trillion is a number that represents 1,000 billion, or 1 followed by 12 zeros (1,000,000,000,000). It is often used to describe large quantities, such as national debts, budgets, or the number of stars in the universe. For example, the United States national debt is often measured in trillions of dollars. In everyday terms, if you were to count to a trillion at one number per second, it would take you over 31,000 years to reach that number. This illustrates just how vast a trillion is, making it difficult to comprehend in practical terms.