In choral and organ arrangements, a "solid" feature generally refers to a strong, driving accompaniment line or a firm cantus firmus bass pedal holding the traditional melody together.
If you are looking for physical goods or specific media characterized by "solid" construction featuring this tune, here are a few possibilities: 🎁 Musical Giftware adeste_fideles
If you are referring to a heavy, physical ("solid") audio format, the track is featured as a staple on heavyweight pressings, such as vintage 78 RPM shellac records from Oxford Records or Decca on eBay . In choral and organ arrangements, a "solid" feature