AM Best rating is summarised as under:

A++, A+
Superior

A, A-
Excellent

B++, B
Good

B, B-
Fair

C++, C+
Marginal

C, C-
Weak

D
Poor

E
Under regulatory supervision

F
In liquidation

S
Rating suspended

Modifiers
u modifier
Under review (typically within 6 months)

pd modifier
Rated based on data in the public domain

s modifier
Rating assigned to a Lloyds' Syndicate

Outlook:
Positive, Negative & Stable outlook, depending on the trend for the next few months.