A life annuity is a financial contract in the form of an insurance product according to which a seller (issuer)—typically a financial institution such as a life insurance company—makes a series of payments in the future to the buyer (annuitant) in exchange for the immediate payment of a lumpsum (single-payment annuity) or a series of regular payments (regular-payment annuity), prior to the onset of the annuity. The payment stream from the issuer to the annuitant has an unknown duration based principally upon the date of death of the annuitant. At this point the contract will terminate unless there are other annuitants or beneficiaries in the contract, and the remainder of the fund accumulated is forfeited. Thus a life annuity is a form of longevity insurance, where the uncertainty of an individual's lifespan is transferred from the individual to the insurer, which reduces its own uncertainty by pooling many clients. Annuities can be purchased to provide an income during retirement.