What does "sociological relativism" mean?

Cultural relativism is a much employed term in cultural anthropology. Starting from the empirical observation that cultures are different, cultural relativism infers the normative conclusion that each culture is equally valid. From this conclusion, the methodological rule of studying each culture in its own right is being deduced.
But the term "sociological relativism" is not so often used. Does it make sense to speak of "sociological relativism"?