An Annuity is commonly known as a pension. It gives you at guaranteed level of income in retirement. The level of pension paid will depend on the age you retire at, your life expectancy, current annuity rates and the value of your pension fund at retirement. Income from an annuity is provided for as a long as you live.
Once an Annuity is purchased it cannot be reversed. When you die your annuity payment stops unless you have added a spouse or civil partners element to the annuity at inception.