Merit Rating Plan is a common term used by insurance companies and state regulators. In general this is something used by insurance companies to define how they might increase or decrease insurance rates.
In the world of car insurance, a merit rating plan would look at the driving record of the insured. If you have a history of accidents or traffic violations, that would lead to increases in your premiums. If you have a clean record that would then hopefully lead to decreases.
Massachusetts refers to its system as the Merit Rating Board.
Delaware and Pennsylvania use the term for workers compensation: Compensation Rating Bureau for DE and PA.
We have seen the term used in the back of car insurance policies in New York State and it is also important in New York Medical Malpractice Insurance. The term does not appear to be used much in Florida, however.