Cultural relativism is the idea that no one culture is superior to another. As Boas, quoted in enotes reference: cultural relativism states
"...civilization is not something absolute, but ... is relative, and ... our ideas and conceptions are true only so far as our civilization goes" (enotes reference, cultural relativism).
In other words, if I believe in God, because I do or because I was raised in a culture that believed, that does not make me superior or inferior to an atheist or person who doesn't believe in God. A person can believe whatever he or she feels is right, but should not impose the culture on others.
Cultural relativism is important in studying other cultures because first and foremost we have to realize we have a bias when we study another culture. Boas also said, "scientists grow up and work in a particular culture, and are thus necessarily ethnocentric" (enotes cultural reference, methodology). We cannot let that bias interfere with the study of the culture, because just because the culture is different from our own does not make us superior or inferior. You can compare and contrast cultural points, but you can not pass judgement upon them.
This can be difficult when we see a culture that seems to limit people's rights, those which we consider important and universal. Universal does not exist in the lens of cultural relativism.