The idea that a majority of people do not express their opinions publicly. In doing so, they are drowned out by a ‘vocal minority’ who get more attention from politicians and the media.
The term was popularized by Richard Nixon in 1969, when he described the Americans who did not protest the Vietnam War. He (correctly) believed that the majority of Americans supported him, and that media coverage of protests gave the impression that the war was unpopular.
Chris Cillizza: “It was seen by Nixon supporters as a populist call for conservatives to rally to his side amid the protests (and the counter-culture) movement that was growing in voice and support at the time. But to Nixon detractors, the term…was racially coded language meant to rally whites against perceived encroaching threats to their culture and way of life.”