Virtually all moral theories end up with a subjective version of morality (including evolutionary explanations of morality), in which moral values have their genesis in the human will in one way or another. In our moral experience, however, we have a basic moral intuition that moral values are objective.
To say a moral value is objective is to say its truth value does not depend on any human knower. So, for example, to say that killing Jews simply because of their ethnicity is immoral in an objective sense is to say that killing Jews is wrong whether anyone believes it to be wrong or not. If Hitler had won the war and eliminated everyone that thought the Holocaust was immoral, such that everyone believed it was moral, it would still, in fact, be immoral.