| The dismal science|
A central bank is a national bank that issues a country's currency, regulates the national money supply and regulates a country's interest rates. Central banks implement a government's chosen monetary policy and are often also tasked with regulating the country's private banks. Usual goals for monetary policy are high employment rate, price stability, and economic growth among other things.
Of course as they belong to the State and have a monopoly on money printing among other things they're not liked by a number of libertarians. You know, those who complain that because of their existence the epoch of the Industrial Revolution was not one of deregulated economies, ignoring why Communism and Socialism appeared in that epoch.