FIRE is an acronym for Financial Independence, Retire Early. The core philosophy of FIRE is to maximize your savings rate (often saving 50% to 75% of your income) and invest heavily in low-cost index funds.
Once your invested assets reach approximately 25 times your annual expenses (known as your “FIRE Number”), you are considered financially independent. At this point, according to the Safe Withdrawal Rate (or 4% Rule), you can theoretically withdraw enough money each year to cover your living expenses indefinitely without ever depleting your principal.