An annuity is an insurance contract - the insurance company invests in stocks and bonds on behalf of the purchaser with the tax deferred money.
When the purchaser turns 65 the purchaser will begin to receive payments, which will fluctuate with the prices of the underlying securities. An annuity will guarantee that the purchaser will receive payments until their death.
Annuity contracts will often carry various charges which vary from one company to another, and would be worth reading before purchasing. Since these are not securities, they are not regulated by the SEC.