A term used by strongly conservative people to describe those with tendings towards socialist policies, such as public healthcare, subsidized housing, etc, and paint them in a negative light.
Somewhat synonymous with communist
in that the sense that Americans use both as insults of sorts.
Jim: Wouldn't it be great if the wealthy were taxed more to accommodate the poor?
Frank: No! Go back to mother Russia you anti-capitalist, red commie SOB!