A Senate runoff is a secondary election held when no candidate receives the required majority of votes in the initial election for a U.S. Senate seat. This situation often arises in states with a large number of candidates, where the leading candidate may only secure a plurality of votes. The runoff typically features the top two candidates from the first election. Runoffs are important because they ensure that the elected senator has broad support from the electorate. States like Georgia and Louisiana frequently use this system, which can significantly impact the balance of power in the U.S. Senate.