To win a primary or caucus, a candidate typically needs a plurality vote. This means they need to receive more votes than any other candidate, but not necessarily more than half of the total votes. In many cases, a majority vote (more than 50%) may be required to ensure a clear winner, especially in some specific types of contests or rules, but a plurality is the most commonly sufficient requirement in many primaries and caucuses.
So, the correct response is plurality vote.