"goodness" itself cannot be defined

Naturalistic Fallacy [Internet Encyclopedia of Philosophy] Moore argues that "goodness" is a foundational and unanalyzable property, similar to the foundational notion of "yellowness," and is not capable of being explained in terms of anything more basic. We intuitively recognize goodness when we see it, as we similarly recognize yellowness when we see it. But the notion of "goodness" itself cannot be defined.