an American rating organisation, which gives a rating showing the reliability of a debtor organisation (its ratings run from AAA to C). It also issues ratings on municipal bonds, running from MIG1 (the highest rating) to MIG4. nounan American rating organisation, which gives a rating showing the reliability of a debtor organisation (its ratings run from AAA to C). It also issues ratings on municipal bonds, running from MIG1 (the highest rating) to MIG4.See alsoStandard & Poor's