Collectivism is a philosophy that considers the citizens of a nation to be a collective, rather than an individual, and subservient to the "whole." The fact that this isn't really logical makes little difference (am I "the People/Proletariat/Volk" or are you?)

It's opposite is individualism, and the political corollary, a society that enshrines political individual rights.

Collectivism encompasses both right-wing and left-wing totalitarianism and authoritarianism. The rhetoric is usually almost identical, if you look.

Collectivism, by its nature, devolves into dictatorship, because when all is said and done, eventually only the State/Leader can stand for the collective.

Even if you don't buy the philosophy, you have to admit the empirical experience of a hundred years of nations under such systems. Communism, for example, has had exactly the same results everywhere it's been tried, despite an enormous variation in races, cultures, environments, geography, language, and history. In cases like East/West Germany or North/South Korea, we had almost a perfect laboratory experiment which minimized all the variables except the selection of a governing principle. I'd say the verdict was in years ago.