Credit rating of country - high, good, speculative or bad

What credit rating of country is considered as high, good, average, speculative or bad ? What does low credit rating mean ?

There are many credit rating agencies in the world and all of them don't use the same ratings. Probably the best known agencies are: Standard & Poor's (S&P), Moody's and Fitch Group.

The highest rating is:
AAA / Aaa

High ratings are:
AA+, AA, AA- / Aa1, Aa2, Aa3

Good ratings are:
A+, A, A- / A1, A2, A3

Lower ratings are:
BBB+, BBB, BBB- / Baa1, Baa2, Baa3

Speculative ratings are:
BB+, BB, BB- / Ba1, Ba2, Ba3
and all the ratings "below" these ones