Social democracy grew out of the differences between communism and socialism.
Communism and socialism were very similar until a group of socialists called democratic socialists began to reject the principles of communism. The democratic socialists did not agree with the way the communists used violence and revolution to gain control.
Communists began to aim more at government power, while socialists concentrated on fair distribution of products and equality for all classes.
Communists think that all means of production or any material necessary for life should be freely shared by everyone, while socialists leave some control with private businesses.