Read literally, a planned economy in the hands of a democratic government, I think. But then other dictionaries substitute "worker" for "social," et cetera, which would lead to broader definitions.
As far as it's actually used, "socialism" is about as useless as a word gets. Who's pretending that Sweden, the Soviet Union, and Anarchist Spain had anything in common that they didn't share with every other society to exist? And that's just among the definitions proferred by people who actually claim to like what the word signifies, whatever it does.