A swing state is defined as a state where the presidential election outcome is uncertain, often characterized by closely contested races. The discussion highlights that swing states can significantly influence the election results due to their Electoral College votes. For instance, Florida was a notable swing state in the Gore-Bush election, where the winner prevailed by a narrow margin. The Electoral College system allows states to determine how their votes are allocated, with most states awarding all their votes to the candidate who wins the majority. In tight races, small shifts in voter percentages can lead to substantial changes in electoral outcomes, making swing states crucial for candidates' campaign strategies. States with close voting percentages, such as those around 51%-49%, receive more attention from candidates, as minor changes in voter sentiment can alter the election's trajectory.