Plausible deniability are words first used by the Central Intelligence Agency (CIA) during the Kennedy administration. In that case it meant not to tell senior government officials about illegal CIA activities. These officials could then defend themselves if the activities were discovered. They would be able to say quite plausibly, and perhaps truthfully, that they did not know anything about it (deniability). It meant that actions of the CIA could not be blamed on the President of the USA.