Words have meaning, and they also evolve. You'll have a much easier time understanding others' meaning and communicating with them in kind if you recognize that in many contexts:

- Social democracy has largely been associated with the word socialism.

- Communism has largely been associated with the word socialism. (Side-note: this is the association you appear to be making; many communists would wholesale reject the notion of the state seizing the means of production, or for that matter the notion of the state as a legitimate institution.)

- Communism basically doesn't exist in the broader vocabulary, except as an historical marker for the Soviet Union, and a geopolitical classification of countries like China or Cuba; to the extent it can be associated with any word today, it's anarchism and only among self-identifying anarchists.

- Anarchism has always been aligned with communism except in terms of the question of the state.

- Big-L Libertarians are largely an ideological faction of the right-wing/Republicans.

- Democrats and Republicans occupy a narrow spectrum of corporatism (though that is increasingly expanding rightward).

- Small-l libertarians are more frequently associated with the word anarchism, which is resented by pretty much everyone who cares.

(Full disclosure since at least my clarity if not my characterization displays a bias: I am an anarchist, of the communist variety, and I tend to view social democracy as harm reduction.)