Put simply this is a death benefit that in the event of your death before a chosen period of time. Eg 10 years. Your payments will continue to be paid until the end of the guaranteed term. Please remember this is a death benefit in case you die early. If you live for 30 years, your annuity payment will continue until the day you die.
An annuity will pay out for the whole of your life. However you can also choose for your income to be guaranteed for a minimum period of time (usually five or ten years), even if you die before then. This means if you die before the end of your guarantee period, the remaining payments left under the guarantee will be paid to your estate.
Source: Iress – Healthy Male Annuity for £50,000 on 31.7.2023.