An annuity is a financial product offered by insurance companies that provides a guaranteed stream of income over a specified period of time, often in retirement. Individuals make either a lump-sum payment or a series of payments to the insurance company, and in return, they receive regular payments back, either immediately or at a later date. Annuities can offer tax-deferred growth, meaning earnings on the investment are not taxed until withdrawn, and they can provide a reliable source of income for retirees to supplement other retirement savings like pensions and Social Security.