An Art Track is an automatically generated YouTube version of a sound recording. An Art Track consists of the sound recording, the album art, and metadata about the recording, such as its title and artist name.
The purpose of Art Tracks is to provide a single official, label-sanctioned YouTube version of every sound recording. 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 that don’t have a produced music video.
Every track that is submitted to YouTube Red is posted as an art track and available in the territories that YouTube Red is assigned in.
Art Tracks fill in the gaps to ensure that YouTube has a complete music catalog. They appear in the same places as produced music videos, such as on the YouTube topic channel for the main artist, in album playlists, and in search results, including watch cards for the artist. YouTube uses the produced music video for recordings that have one; when you upload a music video for a sound recording, the Art Track for that recording becomes unlisted and undiscoverable.
A sample of an art track is below. Through Symphonic, these tracks are created automatically when you select YouTube Red.
More on this from YouTube here.