What is meant by 'Mortgaged Debentures'?

Debentures which are secured against asset/s of a company known as Mortgaged Debenture. Mortgage Debentures are of two types first fixed charge mortgage debenture and second floating charge mortgage debentures.
When debentures are secured against a particular asset, then they are called fixed charge whereas, if the debentures are secured against all the assets of a company, then it is called floating charge. Mortgage debentures can only be sold by the holder when company fails to pay its loan or interest there on.