Gary Poster, with essential assists from Galyn Norwood, Phiroon Phihakendr, Jose Quijada, Pavandeep Kalra. Primaries use secret ballots, similar to those in general elections. Primary voters choose a slate of delegates who are affiliated with a particular candidate. In most states, those delegates sign a pledge to vote at the state convention for the candidate they represent.
Caucuses are less formal and take place in several stages.
Instead of participating in a secret ballot, voters attend regional meetings, where over the course of several hours they listen to delegates stump for the various candidates. In some jurisdictions people still get up and stand single file behind the delegate they plan to support. In later stages of the nomination process, these delegates move on to county or regional caucuses, where they again seek support, and, after two to four lower caucuses, the winning delegates vote in a statewide convention. Each state regulates its primaries or caucuses differently. In some, voters are required to stay within the party with which they're registered when selecting candidates.