A series of equal payments that are made at equal intervals to the owner of an annuity in exchange for investing a fixed amount of cash. The return on an equity-linked annuity is determined by the equity index that it is linked to, such as the S&P 500. Annuities typically are used as an investment tool to plan for retirement. In contrast, the return on variable annuities changes depending on the direction of the equity index that it is linked to.