Conforming loans, also known as "A Paper" loans, make up the majority of loans in the U.S. and are loans that must conform to the guidelines set by Fannie Mae or Freddie Mac in order to be saleable by the lender. Such loans must meet established and strict requirements regarding maximum loan amount, downpayment amount, borrower income and credit requirements and suitable properties. If the lender retains the servicing on these loans they will continue to receive payments from the borrower.

Jumbo loans exceed the loan amount limit for conforming loans.

Loans that do not meet the credit and/or income requirements of conforming loans are known as non-conforming loans and are often referred to as "B", "C" and "D" paper loans depending on the borrower’s credit history and financial capacity. These loans include second mortgages, credit lines, home equity loans and home improvement loans.

Portfolio loans have more flexible qualifying criteria and are sold on the secondary market to Fannie Mae or Freddie Mac or may be kept in the bank’s portfolio.