Capitalism is an economic system based on the private ownership of the means of production.
Socialism is dictated by the common (social) ownership of the means of production, and communism is a subset of socialism that entails absence of money and private property (note: not personal property).
US is blatantly capitalist. Nordic countries are capitalist, too. USSR was socialist, Russia is capitalist; revolutionary regime preceding the creation of USSR was also briefly communist (see: War communism), though, make no mistake, this wasn't the kind of communism anyone wanted, it's just that government couldn't run monetary policy properly at the time and had even bigger issues.