communism" can refer to specific political parties, at its core, communism is an ideology of economic equality through the elimination of private property.
Communism differs from socialism, though the two have similarities. Both philosophies advocate economic equality and state ownership of various goods and services. However, socialism usually works through the existing democratic structures of capitalist countries. Almost all capitalist countries, in fact, have some socialist characteristics, like the public schools and Social Security program in the United States.
In contrast, communists state that capitalist economic and political systems must be completely overthrown through revolution.