A "flip-flop" (used mostly in the United States) or a U-turn (used in the United Kingdom) is a sudden real or apparent change of policy or opinion, while trying to claim that both positions are consistent with each other. Usually it will occur during the period prior to an election in order to maximize the candidate's popularity.

The charge was originally used to attack politicians for making contradictory election policies, while denying the self-contradiction.

Example 1: "Candidate A, after finding out that weapons of mass destruction won't likely be found in Iraq, flip-flopped to keep Candidate B from using his previous stance against him."

Example 2: "During his previous campaign, Candidate B promised to regulate the greenhouse gas carbon dioxide as a pollutant, but declined to do so after taking office. Candidate A could now cite this as a flip-flop."

The charge has more recently been used to attack politicians and in some cases other public figures for any change of policy for any reason whatsoever, including new information becoming available or a change in circumstances. Such changes in policy are considered evidence of a lack of political conviction.

Example 3: "C opposed the treaty on greenhouse gas emissions but has since changed his mind". An opponent of C might describe this as a 'flip-flop' while C might claim that both positions were based on his interpretation of evidence at the time.

This term was used extensively in the 2004 U.S. presidential election campaign. It was used by critics as a catch-phrase attack on John Kerry, claiming he was "flip-flopping" his stance on several issues, including the ongoing war in Iraq. Famously, on March 16 2004 during an appearance at Marshall University Kerry tried to explain his vote for an $87 billion supplemental appropriation for military operations in Iraq and Afghanistan by telling the crowd "I actually did vote for the $87 billion before I voted against it." After the remark became controversial, he explained that he had supported an earlier Democratic measure that would have paid for the $87 billion in war funding by reducing Bush's tax cuts. FactCheck stated that "Kerry has never wavered from his support for giving Bush authority to use force in Iraq, nor has he changed his position that he, as President, would not have gone to war without greater international support."

The term "U-turn" in the UK was famously applied to Edward Heath, Prime Minister of the United Kingdom from 1970-1974. Prior to the 1970 general election, the Conservative Party compiled a manifesto which highlighted free-market economic policies. Heath abandoned such policies when his government nationalised British Leyland (hence the actual "U-turn"). The Conservative government was later attacked for such a move because nationalisation was seen (by the Thatcher era) as antithetical to Conservative beliefs. This later led to one of Margaret Thatcher's most famous phrases: "you turn [U-turn] if you want to; the Lady's not for turning".