"What is a 'grandmaster'?"
In China, there are three levels of mastery recognized by the government. And of these three levels, only forty-six individuals are recognized at a time.
The lowest level of this nationally recognized martial arts skill, is called the "Lohan 18". There are eighteen of these martial artists, picked by the government, for their skill and expertise in either gong fu or wushu. Shi Xing Xi and Shi Xing Hong are two of these eighteen. Interestingly, Shi De Cheng refused the honor.
The next highest level, is called the "Jin Gang", the meaning of which is kind of difficult to translate, as "jin" means "gold", and "gang" means something in-between man and god; i.e., superhuman. There are eighteen of these individuals also, chosen by some nationally recognized society.
The highest level recognized by China, is "Grandmaster". I don't know the Chinese name for it. There are only ten of these individuals in China, and these are considered to be the best. They're also the oldest, as you don't get recognized as a grandmaster unless you are in your seventies, or, above. Age plays a significant role in this. One of China's grandmasters is the headmaster of the Tagou school, in Shaolin village. Interestingly, Shi Su Xi, considered to be, and highly revered as, the grandmaster of Shaolin, is not considered to be a grandmaster of China, but is considered to be the grandmaster of Shaolin.
And don't be fooled by these people that "buy" their titles. Yes, it does happen.