Mortgage is a mechanism under which real estate is used as a security or collateral by the lender. Mortgage in itself is not loan, but it security for the loan that lender makes available to the borrower. In other words we can say mortgage acts as an evidence of debt of the borrower. Residential and commercial are the two broad categories of the mortgage. Depending on the rate of interest mortgage has many variants. Understand them and choose one to fulfill your requirements.