McCarthyism is the practice of making accusations of subversion or treason without proper regard for evidence. It also means "the practice of making unfair allegations or using unfair investigative techniques, especially in order to restrict dissent or political criticism.
McCarthyism began with Senator Joe McCarthy and chief counsel Roy Cohn interrogating suspected communists. At a speech in Wheeling, West Virginia, on February 9, 1950, McCarthy proclaimed that he was aware of 205 card-carrying members of the Communist Party who worked for the United States Department of State.
The term “McCarthyism” first appeared in a Washington Post cartoon on March 29 of that year.
The fear of communism, known as the Red Scare, led to a national witch hunt for suspected communist supporters, which was known as McCarthyism.