This refers to the event in the United Kingdom
when all the members of the House of Commons
must put themselves up for reelection
These days a general election must happen at least every five years. The leader of Her Majesty's Government may call a general election at any time, and in practice they often call it at four years if the conditions are favourable. In fact going to five often indicates that the government is not sure of winning and want to hold onto power as long as possible.
Elections in the UK are traditionally held on a Thursday (I don't know why - probably to cause maximum disruption to the working week knowing polititians).
In the lead up to a general election there is all kinds of shenanigans. The local groups for each major party in each of the constituencies must nominate their candidate (very rarely is the sitting candidate not renominated). However almost anyone who has the deposit and can get the signatures of suffficient constituents can stand in the election.