I was listening to "[REAL ATC] Eastern B737 (candidate Mike Pence) OFF RUNWAY at LaGuardia!"(1) and the LGA Tower asks for and receives reports of braking action from several landing pilots. I assume that this was during inclement weather, such as snow. Several pilots all report braking action as "fair" for their types.
How is "fair" determined? Is it totally subjective, or is there an objective measure? What are the classifications (of braking action) that a pilot can report?
(1) Please note, I did not tag this as LGA, since the question is meant to be a general one, unless each reporting is airport specific.