Final answer:
An open primary is a type of primary election in which voters do not have to disclose their party affiliation and can vote in any party's primary.
Step-by-step explanation:
When voters can vote in either party primary without disclosing their party affiliation, it is referred to as an open primary. In an open primary system, a registered voter may vote in any party’s primary regardless of his or her own party affiliation. This contrasts with a closed primary, where only registered party members can vote in their party's primary, and a run-off primary, which is a second round of voting that is necessary if no candidate achieves a majority in the first round. A blanket primary is a system where voters can participate in all parties' primaries on the same ballot, but it is not commonly used in the United States.