"AAA" and "AA" (high credit quality) and "A" and "BBB" (medium credit quality) are considered investment grade. Credit ratings for bonds below these designations ("BB," "B," "CCC," etc.) are considered low credit quality, and are commonly referred to as " junk bonds .". In total, there are 17 ratings, even though Standard & Poor's only uses four different letters. This is achieved by doubling or tripling letters—the more the better. Ratings can also include a plus sign (which is better than standalone letters) or a minus sign (which is worse than standalone letters). Standard and Poor's AA, A, BBB, BB, and B ratings are sometimes supplemented with a plus (+) or a minus (-) sign to raise or lower a bond's position within the group. Moody's applies numerical