The performance of every song in Evoke Music is tracked and scored using various engagement metrics such as download and bookmarks.
How to see the Popularity Score
1. Select a collection, choose a soundtrack and press the rightmost button. Press "View Pack".
2. You will be seeing the popularity on the right-hand side.
A high popularity score indicates that the song has high engagement. Since more people have engaged with the song (ie. downloaded/bookmarked), the song could potentially be already popular online and therefore familiar.
If you're after an unearthed gem, a high popularity score is not what you're after.