Credit ratings, which are typically expressed in letter grades, apply to businesses and governments and can dramatically affect their costs of borrowing when they issue bonds. They are dished out by agencies such as Standard & Poor’s, Moody's and the Fitch Group. Anything below BBB- grade is considered higher risk, or in the polite industry parlance - "high yield". In impolite industry code, they're called "junk" bonds. The top grade is AAA.