A closed primary is a type of election system in which only registered members of a particular political party are allowed to vote in that party's primary. In other words, it means that voters must declare their allegiance to one of the participating parties and can only cast their ballot for candidates within that specific party. This system helps to ensure that only those who truly support a certain candidate or ideology have a say in selecting the nominee for an office. Closed primaries are often used as a way to maintain the integrity of a political party's platform and prevent members from being swayed by candidates from other parties during the primary process.