Communism is a socio-political ideology that believes people should not own private property; all things should be held in common (the root of the term). Communism as a developed ideology has been around for centuries. Sir Thomas More utilized key components of communism in his theoretical description of an ideal society, Utopia, in his book by the same name. Many scholars also believe that the earliest human communities were communal.
The Common Misconception
Communism is often, especially in the United States, incorrectly associated with dictatorships and other tyranical absolute governments. This association no doubt stems from the dictatorial reigns of Vladimir Lenin and his successor Joseph Stalin over the Soviet Union following the Bolshevik revolution early in the 20th century. Lenin, Stalin, and many of their successors claimed to be communists themselves, and to be leading their country to a communist system based largely on the works of Karl Marx. In reality, Marx's adaptation and interpretation of communism, appropriately called Marxism, is something of a corruption of true communist ideals, and most of the practices implemented in the Soviet Union were nothing short of a perversion even of Marx's twisted concepts.
The key conflict between communism and Marxism, Leninism, and Stalinism, is that communism proposes that there is no private property because either everybody own everything, or nobody owns anything. In the latter three ideologies, this idea is perverted to justify national governmental ownership of everything, presumably by making the incorrect assumption that "public" and "government" are synonomous.