What exactly is Communism?

Communism is a revolutionary socialist movement to create a classless, moneyless and stateless social order structured upon common ownership of the means of production, as well as a social, political and economic ideology that aims at the establishment of this social order.

This movement, in its Marxist–Leninist interpretations, significantly influenced the history of the 20th century, which saw intense rivalry between the "socialist world" (socialist states ruled by communist parties) and the "Western world" (countries with capitalist economies).