What is the spiral of silence?

This is a psychological effect widely known in political science and sociology; a person who believes that he or she is in the minority is the least likely to express their opinion, if it is different from the one the majority has, because of fearing revenge or isolation. The more people consider themselves a part of a minority, the wider the spiral becomes. As people often tend to evaluate public opinion based on their innate “statistical” feeling (which often has nothing in common with reality) spirals of silence sometimes obtain enormous scales.