The term McCarthyism has, as Ellen Schrecker writes, a definition as controversial as McCarthy himself. It could refer specifically to the senator's pattern of reckless, unsubstantiated accusations of communist subversion and declarations of guilt by association for individual political gain. Or it could be used more generally to apply to zealous pursuit of communists, often compared to "witch hunts," targeting labor unions, the Hollywood film industry, government departments, and private organizations in the decade following World War II.

Source: Eric Foner and John A Garraty, eds., (Boston: Houghton Mifflin Company, 1991), pp. 709-710.