An Art Track is an automatically generated YouTube version of a track on a music album. An Art Track consists of the sound recording and the album art.
The purpose of Art Tracks is to provide a YouTube version of every track on every album. Currently, official music videos are available for recordings only when a label or artist invests (non-trivial) time and resources into producing one. Art Tracks automate the creation of versions for recordings even if they don’t have a produced music video.
YouTube creates one Art Track for each track that you upload using the YouTube Music DDEX feed or the "Audio - Art Tracks" bulk upload spreadsheet. It identifies tracks based on their ISRC, release identifier (UPC, EAN, GRid), and partner. YouTube will create Art Tracks for each unique combination of these fields.
Art Tracks ensure that YouTube has a complete music catalog and appear in album playlists and in search results.
Comments on Art Tracks
If you have an Official Artist Channel, you can have comments shown on Art Tracks on your official channel. To do that, select “Allow all comments” or “Hold potentially inappropriate comments for review” as your channel’s comment setting in Studio (Settings 
Once the channel’s comment setting is set to “Allow all comments” or “Hold potentially inappropriate comments for review,” you’ll be able to select Remove next to a comment on your Art Track to hide the comment.
Comments on automatically generated Art Tracks are turned off if the primary artist doesn’t have an Official Artist Channel.