A financial benchmark which is intended to measure the mortgages' overall value made to borrowers with weak credit or subprime. The ABX index employs credit default swap contracts to derive the overall value which is made up of 20 bonds, comprised of subprime mortgages groups. Financial institutions, with the help of this index, are able to determine if whether the market for these securities are worsening or improving. Also know as Asset-Backed Securities Index.