Short answers, pulled from the story.
McCarthyism was a period of political repression and persecution targeting left-wing individuals, driven by fears of communist and Soviet influence on American institutions, running from the late 1940s through the 1950s. It is also called the Second Red Scare or the McCarthy era. The term was first published on the 28th of March 1950 in the Christian Science Monitor.
McCarthy launched his public campaign with a speech on the 9th of February 1950 to the Republican Women's Club of Wheeling, West Virginia, in which he claimed to hold a list of 205 known communists working in the State Department. The speech generated immediate and widespread press attention.
The Hollywood Ten were ten film industry workers, including screenwriters and directors, who refused to cooperate with the House Un-American Activities Committee in October 1947 and cited the First Amendment. Two received six-month prison sentences and the other eight received one-year sentences for contempt of Congress.
Hoover, as FBI director, designed President Truman's loyalty-security program and supervised its investigations, growing the bureau from 3,559 to 7,029 agents between 1946 and 1952. He ran a secret "Responsibilities Program" from 1951 to 1955 distributing anonymous documents to trigger firings, and formalized the COINTELPRO program in 1956, which operated until 1971.
The Warren Court issued a series of rulings beginning in 1956 that reversed key legal pillars of McCarthyism. Key decisions included Slochower v. Board of Education (1956), Yates v. United States (1957), Watkins v. United States (1957), and Kent v. Dulles (1958), which collectively limited loyalty-review firings, reversed communist convictions under the Smith Act, curtailed HUAC's contempt power, and blocked passport denials based on communist beliefs.
Hundreds of people were imprisoned and an estimated ten to twelve thousand lost their jobs. In 1958, roughly one in every five U.S. workers was required to pass some form of loyalty review. The lavender scare, a parallel campaign targeting suspected homosexuals, resulted in over 5,000 federal workers being fired.
Historian Ellen Schrecker argued that J. Edgar Hoover was more central to the anti-communist apparatus than McCarthy, designing the loyalty programs, directing illegal surveillance, and running covert disruption campaigns. Schrecker wrote that had the FBI's conduct been known in the 1950s, the era would likely carry Hoover's name, not McCarthy's.