An October Surprise is any real or rumored dramatic act of the United States government, that the government deliberately times for the month of October to affect the outcome of a federal election. The usual context is that of an election for President of the United States. But October Surprises could also affect mid-term elections. (Presidents stand for re-election in four years, but the House of Representatives and one-third of the Senate stand for re-election every two years.)
In the 1980s, US National Security consultant Gary G. Sick accused then-Candidate Ronald Reagan and his Vice-Presidential running mate, George H. W. Bush, of deliberately provoking (or somehow bribing) the Islamic Republic of Iran to delay releasing the 52 hostages that sympathetic militant university students had taken at the former United States Embassy in Teheran. Sick coined the phrase October Surprise in the book he wrote setting forth his allegations.