The phrase originated in the United States (US), where it can mean a meeting of members of the political party in the US Congress or other similar representative organs of government to select candidates, plan policies, and so on.
Candidates in some states are chosen at a large state meeting called a "Caucus," or at smaller meetings called "primaries".
Caucuses differ from primaries in that voters must attend a meeting to participate in the nominating process.
For more information about the caucus, refer to the link below:
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