Ratings of banks are usually assigned by credit rating agencies such as Standard & Poor's, Moody's and Fitch Ratings. Central banks and supervisory institutions assign their own ratings, such as the Federal Reserve System's CRA rating.
Rating agencies estimate bank credit risk, and they use letter designations to label different levels of the default probability. Higher grades are intended to represent a lower probability of default. Other international agencies, such as DBRS or Morningstar, publish their ratings online as well.
The FED runs the CRA examination process, and financial institutions eventually receive one of the ratings of performance. The online database provides rating information dating back to 1990 for banks examined by the FED.