Mortgage modification is a process where the terms of a mortgage are modified outside the original terms of the contract agreed to by the lender and borrower (i.e mortgagor and mortgagee). In general, any loan can be modified.
Background
In the normal progression of a mortgage, payments of interest and principal are made until the mortgage is paid in full (or paid off). Typically, until the mortgage is paid, the lender holds a lien on the property and if the borrower sells the property before the mortgage is paid-off, the unpaid balance of the mortgage is remitted to the lender to release the lien. Generally speaking, any change to the mortgage terms is a modification, but as the term is used it refers to a change in terms based upon either the specific inability of the borrower to remain current on payments as stated in the mortgage, or more generally government mandate to lenders. A loan modification will typically result in the change to the loan's monthly payment, interest rate, term or outstanding principal.