That is just a term which the left wingers use in order to to surreptitiously "wrest, by degree, all capital from the bourgeoisie, and to centralize all instruments of production in the hands of the state…" , aka, Communism.
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No, what you describe is Communism, not Social Democracy. You don't have a full understanding of what the term means if you think the two are equal. Let me give you some bullet points.
-A Communist wants everyone to have equal income. A Social Democrat wants everyone to have equal opportunity to earn income.
-A Communist wants to take all the rich people's money and assets by force. A Social Democrat acknowledges that there will always be rich and poor people, and so wants the rich to pay higher taxes because they earn more.
-A Communist wants to nationalize all industry and production. A Social Democrat may not want any nationalization, but if he does, it will only be industries that people literally can't live without, reasoning that the forces of supply and demand are unfair when we can't stop demanding a product/service out of necessity.