The Standard and Poor's Corporation (also: S&P), a subsidiary of McGraw-Hill[?], is a company that performs financial research and analysis. It is best known for its S&P 500stock market index. The company also ranks the credit-worthiness of borrowers using a standardized ratings scale.
The basic ratings are:
AAA
AA
A
BBB
BB
B
CCC
CC
C
CI = past due on interest
D = default
NR
Ratings below BBB are non-investment grade junk bonds.