Conventional mortgage is a loan that is not underwritten by a federal agency. They can be conforming loans, which means that they are underwritten according to standards set forth by Fannie Mae or Freddie Mac, and thus can be easily sold on the secondary market to these entities. They can also be non-conforming loans ( e.g. jumbo loans, no doc loans, etc) which do not conform to the standard Fannie Mae or Freddie Mac guidelines. Usually, before a lender will lend under non-conforming status they will have prearranged for a private lender in the non-conforming secondary market to purchase the loan after it is underwritten.