A parliamentary system is a system of government in which the ministers

Minister (government)

A minister is a politician who holds significant public office in a national or regional government. Senior ministers are members of the cabinet....

 of the executive branch get their democratic legitimacy from the legislature

Legislature

A legislature is a kind of deliberative assembly with the power to pass, amend, and repeal laws. The law created by a legislature is called legislation or statutory law. In addition to enacting laws, legislatures usually have exclusive authority to raise or lower taxes and adopt the budget and...

 and are accountable to that body, such that the executive and legislative branches are intertwined.
Students of democracy such as Arend Lijphart

Arend Lijphart

Arend d'Angremond Lijphart is a world renowned political scientist specializing in comparative politics, elections and voting systems, democratic institutions, and ethnicity and politics. He received his PhD in Political Science at Yale University in 1963, after studying at the University of...

 divide parliamentary democracies into two different systems, the Westminster and Consensus systems.

• The Westminster system
  Westminster System
  The Westminster system is a democratic parliamentary system of government modelled after the politics of the United Kingdom. This term comes from the Palace of Westminster, the seat of the Parliament of the United Kingdom....
  
   is usually found in Commonwealth of Nations
  Commonwealth of Nations
  The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...
  
  , although it is not universal within nor exclusive to Commonwealth countries.