Definitions of annuity
a fixed payment made to someone every year, usually until they die
If you have the option of a lump-sum payment or an annuity, you face an excruciating (=very difficult) choice.
a type of investment where an investor pays an initial principal in return for cash payments each year, usually for a specified period or for the lifetime of the annuitant; a cash payment made as a return on such an investment
Your employer may offer a 403(b) pension plan or a tax-sheltered annuity.