1. A portmanteau: communard = Communist + retard. Usually a pejorative. But always true.
2. A synonym for 'Communist'. Since a Communist is always a retard, a communard is the same thing as a Communist.
Person A: "There's 'love' in revolution! (albeit spelled backwards!) Power to the people! Long live Chairman Mao! Everyone is equal. Money is bad. Capitalism sucks. Workers of the world unite! I masturbate to pictures of Che Guevara!"
Person B: "Shut up, you communard."
In this example, Person A is, quite clearly, a communist and a retard, and thus a communard.