A term in which its true meaning has been completely obscured. It is used to attack the credibility of people who seek the truth within crimes committed by the government. It used by those committing the crimes to make those who seek to expose them seem crazy and wrong.
The witnesses who heard a gunshot and saw smoke coming from the grassy knoll during the Kennedy assassination are conspiracy theorists. The witnesses who felt, heard, saw, and where harmed by explosions during the attacks on the World Trade Center towers basement levels on September 11, 2001 are conspiracy theorists. Any who believes the government doesn't love you is a conspiracy theorist.