When you take a mortgage that is higher in value than the current debt secured against the property, which allows monies to be released to the owner. The reasons vary but it could be for debt consolidation, further property investment, improving a property, business purposes, etc. More recently in the UK the term has come to prominence due to a range of Lenders offering specialist products that allow older homeowners to access the Equity in their homes now. These loans are typically not serviced and instead interest is rolled up. The debt is repaid when the owner sells the property or dies.