Final answer:
A closed primary is an election where only registered members of a political party can vote to select the party's candidates, ensuring that nominees are chosen by genuine party supporters.
Step-by-step explanation:
An election in which only registered members of a political party are allowed to participate in selecting a candidate to represent the political party is known as a closed primary. In a closed primary, the ability to vote in the party's primary election is limited to those who are registered party members, which prevents members of other parties from voting to influence the selection of the opposition's candidates. As opposed to an open primary in which any registered voter can participate, regardless of party affiliation, a closed primary ensures that candidates are chosen by true party supporters. This system is considered as one way to preserve party purity and prevent electoral manipulation such as raiding, where voters from one party cross over to influence another party's primary.