The re-mortgaging of property already mortgaged. This is the province of the fringe finance companies. As the original mortgagee holds the security, usually the title-deeds, the second mortgage carries a high risk, which is reflected in high, sometimes very high, interest rates. Such mortgages should be registered with the Land Registry, but the holder of the original first mortgage will have the greater security. However, registration does protect the second mortgagee from the claims of subsequent creditors, secured on the same property.
Reference: The Penguin Business Dictionary, 3rd edt.