It was the Venerable Jigoro Kano, the founder of Judo, who first used the black belt ranking in martial arts.
When one masters the fundamentals of techniques, one can be promoted to the first degree black belt rank. One can be promoted up to the fourth degree based on technical ecellence. And by one's maturity of technique and dedication to the art, one can be promoted to the degrees of fifth and higher. The highest rank, 9th degree, is only given after one has studied the art throughout one's life and achieved maturity (over 60 or 70 years old).
There is a famous story that Kano issued a 10th degree black belt to one of his deceased students, saying "you are now in another world." Since then among martial arts practitioners, it is said that 10th degree means "you are going to another world."
It is quite unfortunate that there are some people promoted to 10th degree black belt while still in this world. The worst ones are those promoted while they are still young, sometimes before their 50's. In these cases, we have to think that their arts are already mastered by them and there is no more room for improvement. IN other words, they have stagnated while in this world. In essence, to be stagnated means that one is dead in the art. Humility, thinking that one is never finished with learning or studying, is one of the iomportant aspects of maturity in the Japanese sense.
Who are 10th degree black belts? They are usually heads of small organizations. Who promotes them? They are promted by their own committees. Why? In order to impress people who are ignorant in the field, and to compete in reputation with larger organizations.
Those that are impressed by still living 10th degree black belts are simply judging a book by its cover.
From Kitoh Karate by S. Sugiyama, copyright 1994.