• It seems to me that Herskovits was trying to say that what's morally good, bad, right or wrong, varies with culture. We could define ethical relativism as the notion that ethical evaluations are all relative to a cultural context. Polygamy is wrong in American culture but right in some west African cultures.
• My other thought is that we could define ethical relativism as the notion that good, bad, right or wrong vary with circumstances. For example, lying is usually wrong, but under special circumstances it isn't. Killing someone is wrong in most circumstances, but it is acceptable if someone attacks you first.

Is that the same thing? I guess not, because circumstances can vary a lot within the same culture and even for the same person over time. I need some help here.