From a Marxist perspective, all class-based societies are governed by dictatorships:
A dictatorship is the political dominance of one group of people over others. In a class society, a dictatorship usually favors the interest of certain classes over the others.
Right now, we live in the Dictatorship of the Bourgeoisie
The bourgeoisie is the ruling class in capitalist society; it owns the means of production and has a decisive influence on production. It lives off of surplus value which it obtains by exploiting the labour power of the proletariat.
Given this thread is about whether or not the Federation is a communist or socialist society, Marxist definitions are the most useful, eh? Furthermore, I'd argue that the term Dictatorship of the Bourgeoisie very accurately describes American (I'm an American) society, and does so regardless of one's personal beliefs.