The Distribution of Ratings displays each of the ratings that reviewers gave your song with their review. You can see how the ratings are spread over a zero to 10 range. Looking at the overall shape of the graph and its' spread will tell you a lot about the appeal of your song.
If the distribution of ratings peak and cluster around a high rating, this would indicate strong consensus and a high Market Potential. If the spread of ratings covers a wide area, this may indicate that reviewers were not as convinced about the song.