{ 1 } - "X is good" means "We'd desire X if we were fully informed and had impartial concern for everyone."
{ 2 } - "Good" means "socially approved." (This is ethical relativism; descriptive relativism claims that different societies disagree about basic moral norms.)
{ 3 } - Imaginary person of supreme moral wisdom (which includes things like being fully informed and having impartial concern for everyone)
{ 4 } - Concluding something (conclusion) from something else (premises)
{ 5 } - Studying very general moral principles

cultural relativism <=> "Good" means "socially approved." (This is ethical relativism; descriptive relativism claims that different societies disagree about basic moral norms.)