What, pray tell, is a special administrative region?

We are spending the final days of our trip in Hong Kong, which occupies a series of islands in South China.  The Chinese government calls it a “special administrative region.” To me it seems like a different country, cleaner and more modern than other places in China. It is a beautiful region, and its citizens seem much less afraid of the government. 

Hong Kong was ruled by the British for 156 years and was returned to the Chinese government 15 years ago. Perhaps because it is prosperous, Hong Kong was allowed to retain its democratic form of government and to keep its own currency. 

Its citizens hold special passports and criticize the government more freely than do the Mainland Chinese.  Information control is not as extreme here as on the mainland, though it is not absent.