Interest Only Mortgages for Equity Release are ordinary mortgages where you take a new mortgage on your property to release a lump sum and the amount is determined by the value of your property and your income.
You then have to pay the interest on that mortgage on a monthly basis for as long as you have the mortgage.
As they are interest only you only pay the interest each month, none of the capital, so the amount you owe remains constant over time.
You can pay off the mortgage at a later stage eg. when you receive a pension payout, encash another investment or if you sell the property.