a period of time, generally characterized as the early to mid 50s, when there was a "communist" scare in the united states. A number of prominent republican politicians (most notably Senator Joe MacCarthy[for whom the term is named] and vice-president Nixon) orchestrated the political "purge" of a number of institutions (most notably, the film industry and the state department) of members suspected to have communist sympathies or "Leftist" thoughts. By simply labling individuals as communist sympathizers, the careers and reputations of hundreds of individuals were ruined. It is now widely accepted that the majority of the victims of MacCarthyism were indeed innocent, and labled only to further the social (anti-Semitic) or political (anti-liberal) goals of those who carried the policy out. But MacCarthy and his sympathizers were able to convice the public that a real and genuine threat actually existed, when in fact there were very few potentially dangerous individuals that were "purged."

When I say, the watchword has changed, I mean it has now become "terrorist" rather than "communist"