The non-hardcore part of the electorate; they often decide an election. It means rhetorical contortions for a US candidate - spouting All The Right Words to the party faithful to win primary elections, but becoming someone else in the general campaign. Swing voters are, in part, the cause of the neverendum - it will always be possible to frame the ballot question to win them; they're the target market for Tony Blair's "Thatcher Lite" and Bill Clinton's "GOP Lite".