Generally, a caucus is a meeting of a political party’s members to choose candidates for office or to form policy. In presidential politics, an informal caucus is a meeting in which potential voters and candidates talk about issues, and then voters decide which candidate they support and which delegates to send to their political party’s convention. In a layered caucus system, loyal party activists decide which candidate they support and select delegates to county meetings, who then select new delegates to state meetings, who then decide which delegates will go to national nominating conventions to select a candidate. The most well-known presidential caucus is the Iowa caucus, an example of a layered caucus. Held in January, the Iowa caucus is the first test for both the Democratic and Republican presidential candidates.
Another use of the term "caucus" refers to a group of legislators who convene to discuss particular issues or pursue common objectives. There are many caucuses in the U.S. Congress, from the well-known, such as the Congressional Black Caucus and the Senate Women’s Caucus, to the more obscure, such as the Congressional Kidney Caucus.