An assessment of the credit worthiness of a borrower given by one of the Credit Rating agencies: S&P, Moody's, and Fitch.
Credit ratings express risk in relative order, giving broadly consistent indicators of relative vulnerability, rather than predictive indicators of actual default rates . Obligations that are highly-rated have lower credit risk than lower-rated obligations, but the individual ratings themselves are not intended to be predictive of a cardinal frequency of default or a percentage expected loss. Source: What Credit Ratings Mean by Fitch Ratings
Some bonds are Unrated, which means an issuer has decided not to pay a credit agency to assess a bond. The reason for such a decision can include the size of the debt issuance, the cost of obtaining a rating, the need (or lack of) for visibility and the complexity (or simplicity) of the issue.
We report the historical default rates and default loss rates observed in the high yield corporate bond market on our Statistics page.