A central bank is a financial institution given privileged control over the production and distribution of money and credit for a nation or a group of nations. In modern economies, the central bank is usually responsible for the formulation of monetary policy and the regulation of member banks.
Examples of central banks:
China - People's Bank of China
United States - the Federal Reserve
European Union countries - European Central Bank
United Kingdom - Bank of England
Note that there is no central bank in Hong Kong. However, the Hong Kong Monetary Authority acts as a central bank and serves some functions of the central bank.