Below-the-line: Term used to refer to any crew members on a film set other than the director, producers, writers and actors. On a standard film budget sheet, those creative personnel are listed at the top; then a line is drawn, and the rest of the crew members and their salaries are listed below the line. More info at Wikipedia
Herb Sorrell: Hollywood union organizer and leader. In the wake of the IATSE scandal, a new union of studio workers was formed, called the Conference of Studio Unions, lead by Herb Sorrell. The CSU set itself up as the clean alternative to the IATSE; it was also the openly leftist alternative, and charges that it was controlled by communists were given credence in 1945, when four factions of the CSU refused to support a set decorators strike, in keeping with the Communist Party's wartime no-strike pledge.
"HUAC": HUAC is the colloquial term used as shorthand to refer to the House Committee on Un-American Activities, which is itself popularly often referred to as the House Un-American Activities Committee (hence, HUAC). HUAC was established in 1938 under Martin Dies as chairman, and famously conducted investigations through the 1940s and ’50s into alleged communist activities. More info at Brittanica.com
IATSE: The International Alliance of Theatrical Stage Employees, or I.A.T.S.E., is a labor union representing technicians, artisans and craftspersons in the entertainment industry, including live theatre, motion picture and television production, and trade shows. During the early 20th century, organized crime gained influence over parts of IATSE leading to corruption and scandal. More info at Wikipedia
Iron Curtain: Term used to describe the political, military, and ideological barrier erected by the Soviet Union after World War II to seal off itself and its dependent eastern and central European allies from open contact with the West and other noncommunist areas. More info at Brittanica.com
Popular Front: Term used to describe any coalition of working-class and middle-class parties united for the defense of democratic forms against a presumed Fascist assault. In the mid-1930s European Communist concern over the gains of Fascism, combined with a Soviet policy shift, led Communist parties to join with Socialist, liberal, and moderate parties in popular fronts against Fascist conquest. More info at Brittanica.com
Premature antifascism: The term invented after World War II to apply (and accuse) anyone who had been concerned about Hitler before the US got into the war. The concept was based on the slightly revisionist idea that only Jews and Communists cared about Fascism before Pearl Harbor happened and put America on the defensive.
Screen Readers Guild: Guild formed by the studio employees hired to read and analyze the production prospects of submitted screenplays. Bernard Gordon, a registered Communist who developed a career during the Blacklist as a writer and producer, was the Guild's president during the 1940s.
Stalinism: Refers to the means of governing and related policies implemented by Joseph Stalin. Stalinist policies in the Soviet Union included: state terror, rapid industrialization, the theory of socialism in one country, a centralized state, collectivization of agriculture, cult of personality, and subordination of interests of foreign communist parties to those of the Communist Party of the Soviet Union—deemed by Stalinism to be the most forefront vanguard party of communist revolution at the time. More info at Wikipedia