An Alt-A mortgage, short for Alternative A-paper, is a type of U.S. mortgage that, for various reasons, is considered riskier than A-paper, or "prime", and less risky than "subprime," the riskiest category. For these reasons, as well as in some cases their size, Alt-A loans are not eligible for purchase by Fannie Mae or Freddie Mac. Alt-A interest rates, which are determined by credit risk, therefore tend to be between those of prime and subprime home loans, although there is no single accepted definition of Alt-A. Typically Alt-A mortgages are characterized by borrowers with less than full documentation, average credit scores, higher loan-to-values, and more investment properties and secondary homes. A-minus is related to Alt-A, with some lenders categorizing them the same, but A-minus is traditionally defined as mortgage borrowers with a FICO score of below 680 while Alt-A is traditionally defined as loans lacking full documentation. Alt-A mortgages may have excellent credit but may not meet underwriting criteria for other reasons. During the past decade, a significant amount of Alt-A mortgages resulted from refinancings, rather than property purchases.