Explain the term ‘two-party system’

The two-party system is a term used in British politics particularly to describe the apparatus of the political system in which two parties, the Labour and Conservative parties, hold the vast majority of the political power in the legislative branch of government. This is evidenced by the fact that out of the 650 seats in the British House of Commons, 559 of them are currently held by Conservative or Labour MPs. The other parties, the Liberal Democrats and the Green Party, to name a few, have a vastly smaller number of seats and have never been considered serious challengers for the two largest parties. The biggest difference in the two-party system between the UK and the US is that while there are third parties who gain a respectable number of seats in the British parliament, the SNP and DUP, in the US almost all elected representatives come from two parties, the Democratic or Republican parties.