A "deleted song" refers to a song that was removed or not included in a final version, usually of a movie, album, or musical. It means that the song was created but ultimately taken out and not released publicly. Full definition
This gesture was previously used to delete songs in a playlist or remove them from the queue. (androidauthority.com)
I was careful not to check the Also delete these songs from iCloud box, because that would have defeated the purpose of this exercise. (imore.com)
Well, that may be a bit of an exaggeration, but you will find deleted songs and a music video of a new version of the classic song Cruella De Vil (starring Selena Gomez). (parentpreviews.com)