Which term describes a primary election open to all eligible voters?

An open primary is a type of primary election that allows all eligible voters to participate, regardless of their party affiliation. This means that registered voters can choose to vote in the primary election of any party without being a member of that party. The significance of an open primary lies in its potential to encourage broader voter participation and engagement in the electoral process, as it provides more flexibility for voters who may feel aligned with a candidate from another party.

In contrast, a caucus is a local gathering of party members to discuss and select candidates, but it does not function like a primary election. A closed primary limits participation to registered party members, thus excluding independent or unaffiliated voters from voting in that primary. The presidential primary refers specifically to the primary elections held to select delegates for presidential candidates, which can be either open or closed depending on the state rules. However, the defining feature of an open primary is its inclusiveness of all eligible voters, making it the correct choice here.