McCarthyism is a term named for Joseph McCarthy, a republican senator from Wisconsin from 1946 to 1957. McCarthyism began, as it is know today, with Senator McCarthy's accusations in February 1950 that Communists had infiltrated the Department of State. He continued to accuse high-ranking officials of treasonous activities for the next three years even though his accusations were never substantiated. McCarthyism is simply the practice of making accusations of political disloyalty with insufficient evidence. The McCarthy Era refers to the wave of political repression in the late 1940's and early 1950's, which targeted the communist party.
McCarthyism itself had begun years before Senator Joseph McCarthy had even come to national attention. The House Committee of Un-American Activities (HUAC), established in 1945 is best known for anti-Communist investigations, called witch-hunts by those who opposed them because of their similarities with the Salem Witch Trials. Blacklisting in the film industry began in 1947 when people were refused jobs because they had been accused of being members of the American Communist Party or having some connection to Communism.
People working in film, television, radio, and theater were fired as a result of the blacklist. The blacklist developed after the HUAC, held public hearings to investigate the influence of Communists in the motion picture industry. Some of the people the committee called to testify as witnesses told HUAC the names of other people who they believed to have Communist connections. Ten of the men called to testify, a group of writers, directors, and producers, refused to tell the committee whether or not they belonged to the Communist Party. They insisted that the committee's questions violated their constitutional rights. The committee decided that they were in contempt of Congress the people who became known as the Hollywood Ten went to prison.
Other well-known examples...