in the US in the 1950s, McCarthyism consisted of searching for and removing from public employment anybody who people thought might be a Communist. Senator Joseph McCarthy was responsible for this process. Many of the people accused were blacklisted (=not allowed to work) or imprisoned. People were encouraged to give the names of their friends and people they worked with to protect themselves. McCarthyism is sometimes used to mean any accusation of disloyalty to your country that is made without proof.