A closed primary is an election system in which people who are members of a particular party are eligible to vote on who should represent that party in an upcoming election. This primary system is in contrast with an open primary, where members of either party can vote for candidates in either party. In the United States, for example, 18 states have closed primary systems, but even then, there may be some special provisions that still allow voters to access the system and vote.
One of the main criticisms of a closed primary is that it excludes independent voters who may want to help choose a possible nominee. These voters are highly sought after, and often can determine the outcome of a general election, where all voters can vote on the full slate of candidates. The closed primary system, therefore, disenfranchises a significant portion of the voting population, many of whom will participate in the general election.
Proponents of closed primaries say it is the members of the parties that have the right to determine who will represent them. Some argue that opening up a party vote to those outside of the party may unduly influence the process. For example, an otherwise weak candidate may be voted as a party's nominee for a position by voters who want their preferred candidate in the opposing party to have an easier time in the general election. These individuals are not interested in the party, but are seeking to possibly sabotage the political process.
Some states have special rules for a primary, which allow independent voters, or even voters of a different party, to register with any party on the day of the election. This means that even if a voter belongs to a different party, if they wish to vote in the other party's primary, they can do so simply by changing registration at the polls. Some may even be able to change back to their preferred party after voting, but will not receive a second ballot. This is very close to an open primary system.
Despite fears of influence from outside sources, a closed primary system is usually attended by party regulars. These individuals are often the ones most dedicated to the party, and often are the most active in it. Therefore, the primary season is often the time for candidates to appeal to party insiders. Once the candidate has emerged from the closed primary, he or she will often change the focus of the campaign toward a broader group of individuals, which is often why many candidates are accused of changing positions in a campaign.