A Parliamentary System is a system of government in which the ministers of the Executive Branch get their legitimacy from a Legislature and are accountable to that body, such that the Executive and Legislative branches are intertwined. 
John Gerring study suggests a strong relationship between parliamentarism and good governance, particularly in economic development and human development.. To the extent that these institutions influence the quality of governance, parliamentary systems may offer advantages over presidential systems of democratic rule.
Parliament is the legislative body of Britain and many other Democratic Nations. Also some Monarchies and Dictatorships have parliaments. In those cases parliament has less power than the king/queen/emperor or dictator.