A secured loan means that a borrower must guarantee an asset as collateral in the case that the loan cannot be repaid. The asset used as collateral must be something of financial value such as a car or more commonly property. A mortgage loans is probably the most common of secured loans and it is used by most people when purchasing property or real estate. A mortgage is usually borrowed from a bank or building society and they are given a lien which is a form of security interest on the deeds to the house until the mortgage debt is repaid. If a borrower defaults on repaying the mortgage the lender will legally be able to repossess the property and sell it in order to recover the debt.
In other cases the collateral for a secured loan might be a car or a possession of similar value. In the same way as a mortgage, if you cannot repay your debt you stand the risk of losing whatever possession you use as collateral so make sure you can afford an unsecured loan before you borrow.