From HowStuffWorks.com:

Most people know what communism is at its most basic level. Simply put, communism is the idea that everyone in a given society receives equal shares of the benefits derived from labor. Communism is designed to allow the poor to rise up and attain financial and social status equal to that of the middle-class landowners. In order for everyone to achieve equality, wealth is redistributed so that the members of the upper class are brought down to the same financial and social level as the middle class. Communism also requires that all means of production be controlled by the state. In other words, no one can own his or her own business or produce his or her own goods because the state owns everything.