Parliamentary opposition is a form of political opposition

Opposition (politics)

In politics, the opposition comprises one or more political parties or other organized groups that are opposed to the government , party or group in political control of a city, region, state or country...

 to a designated government, particularly in a Westminster

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....

-based parliamentary system. Note that this article uses the term government

Executive (government)

Executive branch of Government is the part of government that has sole authority and responsibility for the daily administration of the state bureaucracy. The division of power into separate branches of government is central to the idea of the separation of powers.In many countries, the term...

as it is used in Parliamentary systems, i.e. meaning the administration or the cabinet rather than the state. The title of "Official Opposition" usually goes to the largest of the parties sitting in opposition with its leader being given the title "Leader of the Opposition

Leader of the Opposition

The Leader of the Opposition is a title traditionally held by the leader of the largest party not in government in a Westminster System of parliamentary government...

".

In First Past the Post assemblies, where the tendency

Duverger's law

In political science, Duverger's law is a principle which asserts that a plurality rule election system tends to favor a two-party system. This is one of two hypotheses proposed by Duverger, the second stating that “the double ballot majority system and proportional representation tend to...

 to gravitate into two major parties

Political party

A political party is a political organization that typically seeks to influence government policy, usually by nominating their own candidates and trying to seat them in political office. Parties participate in electoral campaigns, educational outreach or protest actions...

 or party groupings operates strongly, government and opposition roles can go to the two main groupings serially in alternation.