Wave elections in the United States are elections in which a political party makes major gains. Based on the "red states and blue states" color coding convention in use since 2000, wave elections have often been described as either "blue waves" or "red waves" depending on which party makes significant gains, referring to a major increase in seats held by either the Democratic Party (associated with blue) in the former, or the Republican Party (associated with red) in the latter.
Wave elections usually happen during midterm elections.[1] There is no consensus definition of what level of gains is necessary to constitute a wave election,[2][3][4] but the most recent election year widely described as a wave election was 2018's blue wave, where the Democratic Party regained control of the House of Representatives and made a net gain of 7 seats in gubernatorial elections.[5][6]
Midterm
was invoked but never defined (see the help page).