What is a parliamentary system of government?

A parliamentary system is a system of democratic governance of a state in which the executive branch derives its democratic legitimacy from, and is held accountable to, the legislature (parliament); the executive and legislative branches are thus interconnected. In a parliamentary system, the head of state is normally a different person from the head of government. This is in contrast to a presidential system in a democracy, where the head of state often is also the head of government, and most importantly, the executive branch does not derive its democratic legitimacy from the legislature.