A two-party system is a political party system in which two major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term is used to refer to one of two kinds of party systems. Both result from Duverger's law, which demonstrates that "winner-take-all" or "first-past-the-post" elections produce two dominant parties over time.
The first type of two-party system is an arrangement in which all (or nearly all) elected officials belong to one of two major parties. In such systems, minor or third parties rarely win any seats in the legislature. Such systems exist, for example, in the United States, the Bahamas, Jamaica, and Zimbabwe. In such systems, while chances for third-party candidates winning election to major national office are remote, it is possible for factions within the larger parties to exert influence on one or even both of the two major parties.