Communism is both an ideology and a (as of yet) purely hypothetical model of society where there's no state hiearchy, just collective ownership at the local level.
In Marxist-Leninism the socialist state is just a transitional form between a capitalist state and the absence of a state, a communist society. There's a reason why it's called the Union of Socialist Soviet Republics. In theory, the communist party wich ran the whole thing would just give up all its power and let the state wither away

Also this fad of comparing the EU with the USSR is really quite pathetic. Especially when it comes from the same people who (rightfully) complain when Polish nationalists are compared to nazis.