An "open primary election" is a type of election where voters from any political party can participate and vote for their preferred candidate, regardless of their party affiliation. Full definition
Every single constituency must be subjected to a fully open primary election. (conservativehome.blogs.com)
Vermont state law provides for open primary elections, meaning that a voter does not have to be registered with a party in advance in order to participate in its primary. (ballotpedia.org)
While less strict partisanship might be one potential benefit of opening primary elections, Skurnik also points out that there is a question of fairness that should be considered when discussing open primaries. (gothamgazette.com)