A scapegoat is a person or group made to bear the blame for others or to suffer in their place.
It means when you blame someone/group/race etc for something they have not done....as with Hitler & the Jews, he blamed them for loosing the WW1 then used that to gain support and give people a reason for hating them...thus mass extermination.
The word comes from Judaism. During mass reconciliation the rabbi would bring a goat to the alter. The sins of the people would be absorbed into the goat, and it would then be killed, its' blood...