Naturalist fallacy tis defined as the error of defining what is good in terms of what is observable. For example: What's typical is normal; what's normal is good. According to G. E. Moore, Naturalistic Fallacy, is any argument which attempts to define the good in any terms whatsoever, including naturalistic terms; for Moore, Good is simple and indefinable. Some philosophers, most notably defenders of naturalism, have argued that Moore and others are wrong and that such arguments are not necessarily fallacious.
Lexicon of Psychology - Terms, Treatments, Biographies,