Split Rating refers to a situation in which two rating agencies, such as Standard & Poor's and Moody's give two different ratings to the same security. Reason of the different ratings might be due to differences in the methodologies of the agencies.
Additional meaning of Split Rating:
Most regulators do not allow institutional investors to buy bonds that have not received an investment-grade rating from at least two agencies, therefore a split rating in which one agency does not rate a bond investment-grade has major implications for issuers.