What are the orange bars on Amazon Music track lists?

Question

I've just started listening to Amazon Music. (I am an Amazon Prime subscriber.) I've noticed that when I look at a track list for an album, each track has a bar graph indicator with orange bars. What do they mean?

I've shown an example below. They are not progress bars, because I have not yet listened to any of the tracks below on Amazon Music. Nothing happens when you click or hover over the bars with the cursor.

Answer 1

If you inspect the source code of the page you will see that the 'id' of that particular bar is :

'dmusic_tracklist_popularity_B0191V2IIK'

In addition, the 'class' of the column in which it sits is :

'PopularityColumn'

Which implies that, as Dom said, it's the popularity of the track amongst downloaders.