Cultural relativism is the form of moral relativism that holds that all ethical truth is relative to a specified culture. According to cultural relativism, it is never true to say simply that a certain kind of behaviour is right or wrong; rather, it can only ever be true that a certain kind a behaviour is right or wrong relative to a specified society.
The cultural relativist might thus be happy to endorse the statement that it is morally wrong to deny women equality in the work-place in modern America, but would not endorse the statement that it is morally wrong to deny women equality in the work-place. The latter statement implies the existence of an objective ethical standard of the kind that cultural relativism rejects. There are societies, the cultural relativist would say, where for historical and cultural reasons it is acceptable that women are limited in their freedom.
The strength of cultural relativism is that allows us to hold fast to our moral intuitions without having to be judgemental about other societies that do not share those intuitions. If we reject cultural relativism then we face a difficulty: if we are to be consistent about our moral beliefs then it seems that we ought to condemn those past societies that have not conformed to our moral code and perhaps even seek to impose our moral code on those present societies that do not already accept it. This, though, smacks of imperialism, so makes us uneasy.
Cultural relativism allows us to evade this difficulty. On cultural relativism, our moral code applies only to our own society, so there is no pressure on us to hold others to our moral standards at all. On cultural relativism, we can say quite consistently that equality in the work-place is a moral necessity in our society but is inappropriate elsewhere around the globe. In an age where tolerance is increasingly being seen as the most important virtue of all, this can seem to be an attractive position.
This strength of cultural relativism, however, is also its weakness. Cultural relativism excuses us from judging the moral status of other cultures in cases where doing so seems to be inappropriate, but it also renders us powerless to judge the moral status of other cultures in cases where doing so seems to be necessary. Faced with a culture that deems slavery morally acceptable, it seems to be appropriate to judge that society to be morally inferior to our own. Faced with a culture that deems ethnic cleansing morally acceptable, it seems to be appropriate to condemn that society as morally abhorrent.
In order to make such judgements as these, however, we need to be able to invoke an ethical standard that is not culturally relative. In order to make a cross-cultural moral comparison, we need a cross-cultural moral standard, which is precisely the kind of moral standard that cultural relativism claims does not exist.