A caucus is a meeting or grouping of supporters or members of a specific political party or movement. The exact definition varies between different countries and political cultures.

The term originated in the United States, where it can refer to a meeting of members of a political party to nominate candidates, plan policy, etc., in the United States Congress, or other similar representative organs of government. It has spread to certain Commonwealth countries, including Australia, Canada, New Zealand, and South Africa, where it generally refers to a regular meeting of all members of Parliament (MPs) who belong to a parliamentary party: in such a context, a party caucus can be quite powerful, as it has the ability to elect or dismiss the party's parliamentary leader. The term was used historically in the United Kingdom (UK) to refer to the Liberal Party's internal system of management and control.